JavaScript

JavaScript is a very interesting scripting language that has nothing to do with Java.  The name was chosen for marketing reasons.

I think that it can be used as a first programming language in high schools instead of Pascal.  It also can be (should be) used as Windows scripting language. The current version is ECMAScript 5.1.   IE uses JScript 9.0 which has some extensions. Many older browsers support only ECMAScript edition 3.

The Javascript interpreters has a unique feature: they can be configured to accept varying language versions (as in language="JavaScriptXXX").

JavaScript is the only mainstream language that uses a Prototype-based object-oriented implementation (pioneered in Sun Self language). Just because programming language is object oriented it does not mean that it should support classes. Classes are "Aristotelian model" that does not always help to find similarities is a real word. For example, both chess and baseball are games but class model is fruitless to define common properties here.

JavaScript uses a different model called prototype-based programming. Most people use JavaScript without realizing this but this model  supports very powerful constructs, like dynamically attaching behavior to built-in objects via .prototype.  For example if we define the function Employee as:

function Employee () {
   this.name = "";
   this.dept = "general";
}   

We can create object manager that inherits all properties (slots) of the Employee by using statement Manager.prototype = new Employee.

function Manager () {
  this.reports = [];
}
Manager.prototype = new Employee;

function WorkerBee () {
  this.projects = [];
}
WorkerBee.prototype = new Employee;

Proponents of prototype-based programming argues that the use of abstract classes is not a natural way people thing about objects. People thinks in concrete objects and abstract them, not create abstraction first then try to flesh them into a concrete objects.

JavaScript was developed in 1995 by Brendan Eich at Netscape, now a division of AOL. initial name was Lifescript and it was changes to JavaScript for marketing reasons. As a language JavaScript belongs has nothing to do with Java. It is a scripting language like Perl, TCL, Python, etc. See also  NetscapeWorld - JavaScript 1.2's evolution as explained by its creator - May 1997. Here is his own version of events that led to the creation of JavaScript:

I came to Netscape in April 1995, after seven years at Silicon Graphics and three years at MicroUnity Systems Engineering. Netscape was about a year old then and was looking for someone to work on a scripting language or some kind of language inside the browser that could be used to automate parts of a web page or make a web page more dynamic. Java had been around for five years at First Person and Sun, and had been retooled for the web in late 1994. Netscape was the first Java licensee, so the issue became: Can we do just Java, or do we need another language?

There were people who argued strongly that Java's fine for programmers who build components, but there's a much larger audience of people who write scripts or maybe copy a script from somebody else and tweak it. These people are less specialized and may be paid to do something other than programming, like administer a network, and they write scripts part-time or on the side. If they're writing small pieces of code, they just want to get their code done with the minimal amount of fuss. Finally, we agreed that this new language should look like Java, but be a scripting language.

Like all languages, it borrowed from others. LiveScript was the official name it was given when it first shipped in beta releases of Netscape Navigator 2.0 in September 1995, but we rechristened it JavaScript in a joint announcement with Sun on December 4, 1995.

JavaScript attracted a lot of developer attention, because what people wanted back then (and still want) is the ability to go one step beyond HTML and add a little bit of code that makes a web page dynamic - that makes things move, respond to user input, or change color; that makes new windows pop up; or that raises a dialog box to ask a question, with an answer necessary to proceed - things that HTML cannot express. That's really where you need a programming language, but something simpler than Java or C++.

Content creation should not be recondite. It should not be this bizarre arcana that only experts and gold-plated computer science gurus can do. There are economic advantages to lowering the entry costs in creating web content and in sharing it or aggregating it, like Netscape is doing in Web Building.

Calling JavaScript "the glue that holds web pages together" is short and easy to use, but doesn't do justice to what's going on. Glue sets and hardens, but JavaScript is more dynamic than glue. It can create a reaction and make things keep going, like a catalyst.

Paradoxically Microsoft did a lot to promote JavaScript (under the name Jscript). Now Jscript can be used as Windows scripting language but because Microsoft simultaneous promote its VBScript it never got a critical mass.  Javascript can also be used in Microsoft ASP instead of VBscript.

Nevertheless Microsoft OSes are unique in the fact that they permit to use single scripting language for both command line, ASP and HTML scripting.

The Microsoft Windows Scripting Host (WSH) is a tool that allows you to run scripts written in JavaScript making Windows more Unix-like OS with a powerfull shell.  Or more correctly more like OS/2 that used REXX both as a shell and a macrolanguage. The later version is 5.6 and can be freely downloaded from Microsoft. See Downloads.  Microsoft also provides script debugger Download details Script Debugger for Windows NT 4.0 and Later

Using JavaScript in WSH you can now write script to automate common tasks, and to create powerful macros and logon scripts. Microsoft web site (see below) contains several documents that can be downloaded and redistributed at no charge including Jscript reference.

JavaScript is also a pretty interesting macro language, but so far only Lotus Notes uses it in such a role along with its VB clone (LotusScript). Lotus Notes 5.x used JavaScript 1.3 engine licensed from Netscape. Microsoft Office tools are VBA-based.  That might change in 2007 with a new version of Office.   Microsoft provides free  Microsoft Windows Script Control an ActiveX� control that provides developers with an easy way to make their applications scriptable. This, in turn, enables users to extend application functionality through scripts.

Newer versions of JavaScript have good exception handling capabilities. JavaScript 1.4 (which was only around in Netscape's server products) introduced try catch exception handling and throw exception throwing. JavaScript 1.5 which was introduced in IE 5.5 further added the finally clause for try catch.

JavaScript (starting form 1.3) contains the concept of a primitive value undefined. Like in Perl it is represented at the lowest level of language. A variable that has not been assigned a value is of type undefined. As in Perl can use undefined to verify if a variable does not have a value. A JavaScript method or statement also returns undefined, if the variable that is being evaluated does not have an assigned value. undefined is also a property of the global object, whose value is undefined primitive value. Note that under ECMA-262, undefined is only defined as a primitive value and not a property of the global object. In the code below, since the variable input is not defined, the if statement is evaluated to true.

var input;
if(input == undefined){
   document.write("input is not defined.");
}

See What New in JavaScript 1.3. There are a few key concepts to remember when using JavaScript.

• JavaScript is case sensitive. (For the purposes of using a computer you should assume that everything is case sensitive.)
• JavaScript has many reserved words in its syntax. Your scripts won't work correctly if you use reserve words for variable or function names.
• JavaScript event detectors (onMouseOver, onMouseOut, onClick, onLoad, etc.) must be placed inside their respective HTML tags (image, anchor, body, etc.). Only certain event detectors will work with certain HTML tags.
• JavaScript uses a hierarchical structure to organize web page elements. You must reference as far up that structure as your scripts demand.

See also JavaScript 1.5. New features include:

• Runtime errors reported as exceptions.
• Number formatting (Number.prototype.toFixed and Number.prototype.toExponential)
• Regular Expression Enhancements.
• Additional Features (SpiderMonkey and Rhino)
  • Conditional function declaration. (aka Function Expression Statements) [discussion]
  • Multiple catch clauses (aka catchguards.) [discussion]
• Additional Features (SpiderMonkey only)
  • Getters and Setters. [discussion]
  • const keyword.
  • "Strict" mode with new warning messages. [discussion]
  • You can browse the check-in logs and bug reports over the last year, as well as the current open bug list.

The most prominent derivative of JavaScript seems to be ActionScript. by Macromedia. Ever since the release of Flash 5.0, designers have been falling all over themselves to learn JavaScript.  This bold move essentially revived the language that was on decline after Netscape demise. See actionscript_tutorial.zip (1.7MB) for details.

Another wave of interest started with advent of AJAX. From Wikipedia

Ajax (also AJAX; /ˈeɪdʒ�ks/; an acronym for Asynchronous JavaScript and XML)[1] is a group of interrelated web development techniques used on the client-side to create asynchronous web applications. With Ajax, web applications can send data to, and retrieve data from, a server asynchronously (in the background) without interfering with the display and behavior of the existing page. Data can be retrieved using the XMLHttpRequest object. Despite the name, the use of XML is not required (JSON is often used instead), and the requests do not need to be asynchronous.[2]

Ajax is not a single technology, but a group of technologies. HTML and CSS can be used in combination to mark up and style information. The DOM is accessed with JavaScript to dynamically display, and to allow the user to interact with the information presented. JavaScript and the XMLHttpRequest object provide a method for exchanging data asynchronously between browser and server to avoid full page reloads.

In the 1990s, most web sites were based on complete HTML pages. Each user action required that the page be reloaded from the server (or a new page loaded). This process was inefficient, as reflected by the user experience: all page content disappeared then reappeared. Each time a page was reloaded due to a partial change, all of the content had to be re-sent, even though only some of the information had changed. This placed additional load on the server and used excessive bandwidth.

In 1996, the iframe tag was introduced by Internet Explorer to load content asynchronously. In 1998, Microsoft Outlook Web Access team implemented the first component XMLHTTP by client script.

In 1999, Microsoft utilized its iframe technology to dynamically update the news stories and stock quotes on the default page for Internet Explorer and created the XMLHTTP ActiveX control in Internet Explorer 5, which was later adopted by Mozilla, Safari, Opera and other browsers as the XMLHttpRequest JavaScript object. Microsoft has adopted the native XMLHttpRequest model as of Internet Explorer 7, though the ActiveX version is still supported. The utility of background HTTP requests to the server and asynchronous web technologies remained fairly obscure until it started appearing in full scale online applications such as Outlook Web Access (2000)[5] and Oddpost (2002).

Google made a wide deployment of standards-compliant, cross browser Ajax with Gmail (2004) and Google Maps (2005)

The term Ajax was coined on 18 February 2005 by Jesse James Garrett in an article entitled "Ajax: A New Approach to Web Applications", based on techniques used on Google pages.

On 5 April 2006 the World Wide Web Consortium (W3C) released the first draft specification for the XMLHttpRequest object in an attempt to create an official web standard.

The term Ajax has come to represent a broad group of web technologies that can be used to implement a web application that communicates with a server in the background, without interfering with the current state of the page. In the article that coined the term Ajax,[1] Jesse James Garrett explained that the following technologies are incorporated:

• HTML (or XHTML) and CSS for presentation
• The Document Object Model (DOM) for dynamic display of and interaction with data
• XML for the interchange of data, and XSLT for its manipulation
• The XMLHttpRequest object for asynchronous communication
• JavaScript to bring these technologies together

Since then, however, there have been a number of developments in the technologies used in an Ajax application, and the definition of the term Ajax. XML is not required for data interchange and therefore XSLT is not required for the manipulation of data. JavaScript Object Notation (JSON) is often used as an alternative format for data interchange,  although other formats such as preformatted HTML or plain text can also be used.

Drawbacks

In pre-HTML5 browsers, pages dynamically created using successive Ajax requests did not automatically register themselves with the browser's history engine, so clicking the browser's "back" button may not have returned the browser to an earlier state of the Ajax-enabled page, but may have instead returned to the last full page visited before it. A pre-Ajax workaround was to use invisible iframes to trigger changes in the browser's history. A workaround implemented by Ajax techniques is to change the URL fragment identifier (the part of a URL after the '#') when an Ajax-enabled page is accessed and monitor it for changes.

However, HTML5 provides an extensive API standard for working with the browser's history engine.

Dynamic web page updates also make it difficult to bookmark and return to a particular state of the application. Solutions to this problem exist, many of which again use the URL fragment identifier. The solution provided by HTML5 for the above problem also applies for this.

Depending on the nature of the Ajax application, dynamic page updates may interfere disruptively with user interactions, especially if working on an unstable Internet connection. For instance, editing a search field may trigger a query to the server for search completions, but the user may not know that a search completion popup is forthcoming, and if the internet connection is slow, the popup list may show up at an inconvenient time, when the user has already proceeded to do something else.

Because most web crawlers do not execute JavaScript code, publicly indexable web applications should provide an alternative means of accessing the content that would normally be retrieved with Ajax, thereby allowing search engines to index it.

Any user whose browser does not support JavaScript or XMLHttpRequest, or simply has this functionality disabled, will not be able to properly use pages which depend on Ajax. Devices such as smartphones and PDAs may not have support for the required technologies, though this is becoming less of an issue. The only way to let the user carry out functionality is to fall back to non-JavaScript methods. This can be achieved by making sure links and forms can be resolved properly and not relying solely on Ajax.

Similarly, some web applications which use Ajax are built in a way that cannot be read by screen-reading technologies, such as JAWS. The WAI-ARIA standards provide a way to provide hints in such a case.[14]
Screen readers that are able to use Ajax may still not be able to properly read the dynamically generated content.[15]
The same origin policy prevents some Ajax techniques from being used across domains,[6] although the W3C has a draft of the XMLHttpRequest object that would enable this functionality.[16] Methods exist to sidestep this security feature by using a special Cross Domain Communications channel embedded as an iframe within a page,[17] or by the use of JSONP.

The asynchronous callback-style of programming required can lead to complex code that is hard to maintain, to debug[18] and to test. 
 

Dr. Nikolai Bezroukov

NEWS CONTENTS

• 20110711 : Stanford CS101 Adopts JavaScript ( July 11, 2011 , Slashdot )
• 20080708 : GromJS 1.7.2 by Vlajko ( GromJS 1.7.2 , Jul 8, 2008 )
• 20080708 : IBM developerWorks ( IBM developerWorks, )
• 20080708 : The JavaScript Object Model ( The JavaScript Object Model, )
• 20080708 : A. Sundararajans Weblog ( A. Sundararajan's Weblog, )
• 20080708 : Whats New In WSH 5.6 ( What's New In WSH 5.6, )
• 20080708 : Setting up Remote WSH ( Setting up Remote WSH, )
• 20080708 : Ajax (programming) - Wikipedia, the free encyclopedia ( Ajax (programming) - Wikipedia, the free encyclopedia, )
• 20080708 : Wise ASP - JScript Regular Expressions ( Wise ASP - JScript Regular Expressions, )
• 20080708 : Fabulous Adventures In Coding Are JScript strings passed by reference ( Fabulous Adventures In Coding Are JScript strings passed by reference, )
• 20080708 : John ( John, )
• 20080708 : Eric Lippert ( Eric Lippert, )

Old News ;-)

[Jul 11, 2011] Stanford CS101 Adopts JavaScript

July 11, 2011 | Slashdot

"In case further proof were needed that JavaScript shall indeed inherit the earth, we have the news that Stanford has adopted JavaScript to teach CS101 - Introduction to Computing Principles: 'The essential ideas of computing via little phrases of JavaScript code.'

You can even try it out for yourself at Stanford's course page."

sunderland56: First programming course? At Stanford??

Does anyone really get admitted into Stanford without being able to program already?? Reply to This

Kamiza Ikioi:

George Bush got into Yale. Anything is possible.

ccguy:

I'm sure lots of people gets admitted thinking they are able to program.

Dahamma Re:First programming course? At Stanford??

The summary is awful.

First, this isn't even recent news, it was added *last* year.

Second, this isn't an intro course for CS majors (or even any engineering major, or hell, even a non-engineering major interested in programming). It's basically a really high level intro to computers and "programming principles" for "fuzzies" with an irrational fear of computers (which as you say, is definitely a small group at Stanford).

Though the lecturer (Nick Parlante) is awesome, so it's probably a fun class, and might even get some people interested in taking the real intro to programming class (CS106A).

Animats: What's wrong with JavaScript for CS?

It's a reasonable language in its modern form. It has a reasonable, if not great, syntax. (Compare Perl.) Someone wrote that it doesn't support recursion. Yes, it does. It even supports closures. The object model is adequate, if not inspired. It's a memory-safe language. About the only thing it doesn't support is concurrency.

The current generation of JIT compilers do a reasonably good job on performance. Free implementations are easily available. So there's no problem running it.

The problem with Javascript is mostly that the code quality seen on many web pages is appallingly bad. (Or, alternatively, the source code has been run through some obfusicator/compressor.) That's not the fault of the language. Javascript's interface to browsers is also rather clunky; the primitives for manipulating the DOM were ill-chosen. But, again, that's not a language problem.

[Jul 8, 2008] GromJS 1.7.2 by Vlajko

About: GromJS is server-side JavaScript implementation of Mozilla's SpiderMonkey interpreter. It provides Web designers and programmers with the ability to use JavaScript object-based code for creating dynamic pages and Web scripts and to interact with objects on the Web server. For example, it can be used to manipulate files and directories, handle client- sent data and databases, and to create content management systems. It includes support for files, SQLite3 databases, session variables, hash arrays, HTTP file-upload, cookies, pipes, and many other. It currently supports Linux and FreeBSD.

Changes: This release includes an easier installation procedure for the GromJS server-side JavaScript interpreter, a number of new features/enhancements, and additions to the documentation.

IBM developerWorks

NEW! Building JavaScript applications with JSEclipse

Using JSEclipse, JavaScript programmers now have their own Eclipse plug-in that provides many important features to aid in the development of JavaScript applications. JSEclipse gives JavaScript developers the same ease of use that Eclipse has been providing in the Java language and others for years. Learn to use this tool, while creating a colony of evolving "creatures" on your page.
FREE! Go There Now!

The JavaScript Object Model

A JavaScript object has properties associated with it. You access the properties of an object with a simple notation:

objectName.propertyName

Both the object name and property name are case sensitive. You define a property by assigning it a value. For example, suppose there is an object named myCar (we'll discuss how to create objects later-for now, just assume the object already exists). You can give it properties named make, model, and year as follows:

myCar.make = "Ford"
myCar.model = "Mustang"
myCar.year = 69;

An array is an ordered set of values associated with a single variable name. Properties and arrays in JavaScript are intimately related; in fact, they are different interfaces to the same data structure. So, for example, you could access the properties of the myCar object described above as follows:

myCar["make"] = "Ford"
myCar["model"] = "Mustang"
myCar["year"] = 67;

Equivalently, each of these elements can be accessed by its index, as follows:

myCar[0] = "Ford"
myCar[1] = "Mustang"
myCar[2] = 67;

This type of an array is known as an associative array, because each index element is also associated with a string value. To illustrate how this works, the following function displays the properties of the object, when you pass the object and the object's name as arguments to the function:

function show_props(obj, obj_name) { 
    var result = "" 
    for (var i in obj) 
        result += obj_name + "." + i + " = " + obj[i] + "\n" 
    return result; 
} 

So, the function call show_props(myCar, "myCar") would return the following:

myCar.make = Ford
myCar.model = Mustang
myCar.year = 67

Functions and Methods

Functions are one of the fundamental building blocks in JavaScript. A function is a JavaScript procedure--a set of statments that performs a specific task.

A function definition consists of the function keyword, followed by

• the name of the function
• a list of parameters to the function, enclosed in parentheses, and separated by commas
• the JavaScript statements that define the function, enclosed in curly braces, {...}

In a Navigator application, you can use any functions defined in the current page. It is generally a good idea to define all your functions in the HEAD of a page. When a user loads the page, the functions will then be loaded first.

The statements in a function can include other function calls defined for the current application.

For example, here is the definition of a simple function named pretty_print:

function pretty_print(string) { document.write(&quot;</p> <hr> <p>&quot; + string) }

This function takes a string as its argument, adds some HTML tags to it using the concatenation operator (+), then displays the result to the current document.

Defining a function does not execute it. You have to call the function for it to do its work. For example, you could call the pretty_print function as follows:

The parameters of a function are not limited to just strings and numbers. You can pass whole objects to a function, too. The show_props function from the previous section is an example of a function that takes an object as an argument.

A function can even be recursive, that is, it can call itself. For example, here is a function that computes factorials:

function factorial(n) {
  if ((n == 0) || (n == 1))
    return 1
  else {
    result = (n * factorial(n-1) )
    return result
  }
}

You could call this function with an argument of one through five inside a loop as follows:

for (x = 0; x < 5; x++) {
   document.write(x, " factorial is ", factorial(x))
   document.write("
")
}

The results would be:
0 factorial is 1
1 factorial is 1
2 factorial is 2
3 factorial is 6
4 factorial is 24
5 factorial is 120

Methods

A method is a function associated with an object. You define a method in the same way as you define a standard function. Then, use the following syntax to associate the function with an existing object:

object.methodname = function_name

where object is an existing object, methodname is the name you are assigning to the method, and function_name is the name of the function.

You can then call the method in the context of the object as follows:

object.methodname(params);

Using this for Object References

JavaScript has a special keyword, this, that you can use to refer to the current object. For example, suppose you have a function called validate that validates an object's value property, given the object, and the high and low values:

function validate(obj, lowval, hival) {
   if ((obj.value < lowval) || (obj.value > hival))
      alert("Invalid Value!")
}

Then, you could call validate in each form element's onChange event handler, using this to pass it the form element, as in the following example:

<input type="text" name="age" size="3" onchange="validate(this, 18, 99)">

In general, in a method this refers to the calling object.

Creating New Objects

Both client and server JavaScript have a number of predefined objects. In addition, you can create your own objects. Creating your own object requires two steps:

• Define the object type by writing a function.
• Create an instance of the object with new.

To define an object type, create a function for the object type that specifies its name, and its properties and methods. For example, suppose you want to create an object type for cars. You want this type of object to be called car, and you want it to have properties for make, model, year, and color. To do this, you would write the following function:

function car(make, model, year) {
   this.make = make; 
   this.model = model;
   this.year = year;
}

Notice the use of this to assign values to the object's properties based on the values passed to the function.

Now you can create an object called mycar as follows:

mycar = new car("Eagle", "Talon TSi", 1993);

This statement creates mycar and assigns it the specified values for its properties. Then the value of mycar.make is the string "Eagle", mycar.year is the integer 1993, and so on.

You can create any number of car objects by calls to new. For example,

kenscar = new car("Nissan", "300ZX", 1992)

An object can have a property that is itself another object. For example, suppose I define an object called person as follows:

function person(name, age, sex) {
   this.name = name;
   this.age = age;
   this.sex = sex;
}

And then instantiate two new person objects as follows:

rand = new person("Rand McNally", 33, "M")
ken = new person("Ken Jones", 39, "M")

Then we can rewrite the definition of car to include an owner property that takes a person object, as follows:

function car(make, model, year, owner) {
   this.make = make; 
   this.model = model;
   this.year = year;
   this.owner = owner;
}

To instantiate the new objects, you then use the following:

car1 = new car("Eagle", "Talon TSi", 1993, rand);
car2 = new car("Nissan", "300ZX", 1992, ken)

Notice that instead of passing a literal string or integer value when creating the new objects, the above statements pass the objects rand and ken as the parameters for the owners. Then if you want to find out the name of the owner of car2, you can access the following property:

car2.owner.name

Note that you can always add a property to a previously defined object. For example, the statement:

car1.color = "black"

adds a property color to car1, and assigns it a value of "black". However, this does not affect any other objects. To add the new property to all objects of the same type, you have to add the property to the definition of the car object type.

Defining Methods

You can define methods for an object type by including a method defnition in the object type definition. For example, suppose you have a set of image GIF files, and you want to define a method that displays the information for the cars, along with the corresponding image. You could define a function such as:

function displayCar() {
   var result = "A Beautiful " + this.year 
                + " " + this.make + " " + this.model;
   pretty_print(result)
}

where pretty_print is the previously defined function to display a string. Notice the use of this to refer to the object to which the method belongs.

You can make this function a method of car by adding the statement

this.displayCar = displayCar;

to the object definition. So, the full definition of car would now look like:

function car(make, model, year, owner) {
   this.make = make; 
   this.model = model;
   this.year = year;
   this.owner = owner;
   this.displayCar = displayCar;
}

A. Sundararajan's Weblog More JavaScript debugging tips (Mustang context)

This is continuation of my earlier post on the same topic.

1. objects have prototypes

   This is just to remind that objects have a prototype object. JavaScript is prototype-delegation based language. If a property or method is not found in an object, it's prototype is searched. So, when you access obj.x, the property "x" may actually be in the prototype of object "obj" (or prototype of prototype and so on). An object's prototype is accessible by a special property of the name __proto__. Note that this is non-standard Rhino specific extension. Rhino allows you to change prototype by assigning to __proto__ property!

2. scopes are objects

   One more similarity to Lisp! In Lisp, scopes are known as "environments". Scopes are nothing but a map of variable names to variable values. In JavaScript, scopes are objects whose property names are variable names. For example, this keyword in global/toplevel scope refers to the global object. You can walk all global variables by this function:

   function printGlobals() {
for (var i in this) {
println(i + ' = ' + this[i]);
}
}

   Scopes are organized in a parent-child chain. The local scope of a function has the global scope as it's parent. Local variable scope of a nested function has enclosing function's local scope as it's parent and so on. Scope objects are also referred as "variable objects" (i.e., object that keeps variables). The "next" link in this chain is accessible by the special property called __parent__. Note that this is non-standard Rhino specific extension. Rhino allows you to change parent by assigning to __parent__ property! In addition to functions and local functions, with statements also add an innermost scope to scope-chains.

   How can we get hold of the "local scope" object of a function? Note that a nested function's parent scope is the local scope of the enclosing function. So, we can introduce an anonymous local function (with no code) to get it's __parent__.

   
   
   function f() {
      var x = 10;
      // introduce an anonymous nested function just to get 
      // it's parent scope -- which is nothing but scope of
      // this function.
      var localScope = (function() {}).__parent__;
      println(x); // prints 10
      println(localScope.x); // prints 10 again!
   }

   With this knowledge we can write generic code to print all local variables of a function:

   
   var printLocals = "{ var _locals = (function(){}).__parent__;       " +
                     "  for (var _i in _locals) {                      " +
                     "     if (/_locals/(_i) || /_i/(_i)) continue;    " +
                     "     println(_i + '=' + _locals[_i].toSource()); " +
                     "  } " +
                     "}";
   
   
   function h() {
      var x = 32;
      var y = { x : 3 };
      // prints all locals (x, y in this function)
      eval(printLocals);
   }

   Note that I've used eval - I cannot define printLocals as a function -- because to access local scope object of given function (like h() above), I've to define an anonymous function inside the same function! So, I'm eval'ing a string to get hold of the same. But, printLocals is generic -- in the sense that you can eval it any of your function to print all locals of it. Note that although JavaScript is similar to Lisp, macros are not supported. I had to use eval to simulate macro expansion.

   If you combine the fact that scopes are objects and objects have prototypes, we have the following lookup rule for variables:

   1. get the innermost scope object
   2. look for property with the same name as that of the variable
   3. if not found - chase the prototype chain (till null __proto__ is found) and look for it
   4. if not found, then get parent scope and look for property there. (till null __parent__ is found)
   So, each variable lookup is potentially a 2-dimensional search!
   
3. Handling Java Exceptions

   JavaScript exception handling involves try..catch statement. But, exceptions typically are JavaScript Error object or subtypes of it (but other types like string can also be thrown!). If you are getting a Java exception, that is also wrapped as a JavaScript Error object. Sometimes, you may want to get the exact Java exception thrown -- may be the Java method you called throws multiple exceptions and you may want to handle those differently. Rhino adds javaException property to Error objects -- this property is initialized if an Error object wraps around a Java exception.

   
   try {
       var obj = new java.lang.Object();
       obj.wait();
   } catch (e) {
       var exp = e.javaException;
       if (exp instanceof java.lang.IllegalMonitorStateException) {
           exp.printStackTrace();
       } else if (exp instanceof java.lang.InterruptedException) {
           // do something differently..
       } else {
           // something else!
       }
   }
   
   

4. printStackTrace

   In Java debugging, we often use Throwable.printStackTrace() or Thread.dumpStack() to print stack trace. How about similar stack trace for JavaScript? It turns out that Rhino does support stack trace - with script file name, function name and line number!. Rhino adds rhinoException property to Error object. The printStackTrace method on this rhinoException include script functions, line numbers etc.

   File: test.js

   
   function f() {
     g();
   }
   
   function g() {  
     try {
        var c = undefined;
        c.toString();
     } catch (e) {
        e.rhinoException.printStackTrace();
     }
   }
   
   f();
   
   

   The above code prints something like:

   
   D:\>jrunscript  test.ps
   sun.org.mozilla.javascript.internal.EcmaError: TypeError: Cannot call method "toString" of undefined (p.ps#19)
           at sun.org.mozilla.javascript.internal.ScriptRuntime.constructError(ScriptRuntime.java:3234)
           at sun.org.mozilla.javascript.internal.ScriptRuntime.constructError(ScriptRuntime.java:3224)
           at sun.org.mozilla.javascript.internal.ScriptRuntime.typeError(ScriptRuntime.java:3240)
           at sun.org.mozilla.javascript.internal.ScriptRuntime.typeError2(ScriptRuntime.java:3259)
           at sun.org.mozilla.javascript.internal.ScriptRuntime.undefCallError(ScriptRuntime.java:3278)
           at sun.org.mozilla.javascript.internal.ScriptRuntime.getPropFunctionAndThis(ScriptRuntime.java:1968)
           at sun.org.mozilla.javascript.internal.Interpreter.interpretLoop(Interpreter.java:2931)
           at script.g(test.ps:19)
           at script.f(test.ps:2)
           at script(test.ps:27)
           at sun.org.mozilla.javascript.internal.Interpreter.interpret(Interpreter.java:2250)
           at sun.org.mozilla.javascript.internal.InterpretedFunction.call(InterpretedFunction.java:149)
           at sun.org.mozilla.javascript.internal.ContextFactory.doTopCall(ContextFactory.java:337)
           at sun.org.mozilla.javascript.internal.ScriptRuntime.doTopCall(ScriptRuntime.java:2757)
           at sun.org.mozilla.javascript.internal.InterpretedFunction.exec(InterpretedFunction.java:160)
           at sun.org.mozilla.javascript.internal.Context.evaluateReader(Context.java:1163)
           at com.sun.script.javascript.RhinoScriptEngine.eval(RhinoScriptEngine.java:106)
           at javax.script.AbstractScriptEngine.eval(AbstractScriptEngine.java:230)
           at com.sun.tools.script.shell.Main.evaluateReader(Main.java:314)
           at com.sun.tools.script.shell.Main.evaluateStream(Main.java:350)
           at com.sun.tools.script.shell.Main.processSource(Main.java:267)
           at com.sun.tools.script.shell.Main.access$100(Main.java:19)
           at com.sun.tools.script.shell.Main$2.run(Main.java:182)
           at com.sun.tools.script.shell.Main.main(Main.java:30)
   

   Note that the red lines above include script function, file name and line number. With this you can write a generic printStackTrace function as

   
   function printStackTrace(exp) {    
       if (exp == undefined) {
           try {
               exp.toString();
           } catch (e) {
               exp = e;
           }
       }
       // note that user could have caught some other
       // "exception"- may be even a string or number -
       // and passed the same as argument. Also, check for
       // rhinoException property before using it
       if (exp instanceof Error && 
           exp.rhinoException != undefined) {
           exp.rhinoException.printStackTrace();
       }
   }
   
   

   You can call above function whereever you want script stack trace - much like java.lang.Thread.dumpStack() call. You can get fancier output by getting the stack trace into a string and then filtering it to print only the lines that begin with at script -- so that you can view only the script frames in the trace. That is left an exercise to the reader [hint: use printStackTrace that accepts java.io.PrintWriter]

A. Sundararajan's Weblog JavaScript debugging tips (for Mustang context)

Mustang (Java SE 6) is co-bundled with Mozilla Rhino based JavaScript engine as an example implementation for javax.script API.

There are 3 use cases within JDK

• jrunscript - command line script shell
• jconsole script shell plugin
• jhat uses JavaScript engine to implement OQL (SQL-like query language) for heap queries.

There is already an experimental web application environment that uses JavaScript - http://phobos.dev.java.net.

So, we may expect that JavaScript will be employed within the JDK context more often. How about debugging support for JavaScript engine in JDK context? For Firefox, there are atleast two debuggers (that I know of!):

1. Venkman
2. Firebug

Rhino comes with it's own debugger -- but in Mustang, Rhino's tools are not included. Also, javax.script API does not include debugger API (yet?). For Rhino in Mustang, we have to resort to other ways to debug scripts including good old println/printf style. Few debugging tips and tricks are here...

1. Use jrunscript in interactive mode for debugging.

   You can use load function to load your script files (or URLs). In the interactive mode, you can call specific script functions or evaluate various expressions.

2. print or alert debugging!

   Use good old printf/System.out.println/alert/echo style debugging! In Mustang Java, there are built-in print and println functions always defined. If you have scripts that use alert, you can consider defining something like this:

   
      // define alert to be same as println function
      var alert = println;
   
   

   Note that 'print' and 'println' functions print the message to output writer configured in the script context (recall that "context" is a pre-defined variable initialized with the current ScriptContext object). If you configure different output writer (may be, the one that writes messages to a file or socket etc.), you can make all print/println messages to go there.

3. Use Function.toSource() to view source code of various functions.

   
   // viewing function sources in jrunscript prompt.
   
   // built-in functions are shown as "native code"
   // But, you can get arity (number of arguments)
   // of the function
   js> eval.toSource()js> eval.toSource()
   function eval() { [native code for eval, arity=1] }
   
   // for script functions toSource() shows full source
   js> function add(x, y) { return x + y }
   js> add.toSource()
   function add(x, y) {return x + y;}
   
   // for Java methods we get signature as part of "source"
   js> var v = new java.util.Date()
   js> v.getDay.toSource()
   function getDay() {/*
   int getDay()
   */}
   
   // for overloaded Java methods, toSource() shows signatures
   // for all overloads
   js> var out = java.lang.System.out
   js> out.println.toSource()
   function println() {/*
   void println(boolean)
   void println(char)
   void println(int)
   void println()
   void println(long)
   void println(java.lang.Object)
   void println(java.lang.String)
   void println(char[])
   void println(double)
   void println(float)
   */}
   
   

4. JavaScript object fields and array elements can be walked by

   
      for(var i in obj) { print(obj[i]); }
   
   

   like loop.

   I frequently print all fields of an object (or elements of array) this way. Note that you will get object's methods (which are function valued properties) as well. To filter these, you can use typeof operator. You can also filter properties using property name pattern/index.

5. Use JavaScript's support for higher-order functions.

   JavaScript functions can be passed as arguments and returned as values. Functions can be called by apply or call functions. Functions are first-class values that can be stored in variables. You can use these to implement JavaScript AOP. You can use "interceptors" to print debug trace output. For eg. function entry/exit can be printed (along with arguments, if desired). For example, the following is a variation of JavaScript AOP referred in above link..

   
   
   var Aspects = new Object();
   
   // calls "before" interceptor function before calling function
   // name specified by fname. The function is expected to be a property
   // of object 'obj'
   Aspects.addBefore = function(obj, fname, before) {
       var oldFunc = obj[fname];
       var newFunc = function() {        
           return oldFunc.apply(this, before(arguments, oldFunc, this));
       };
       // store oldFunc for restore purpose...
       newFunc.oldFunc = oldFunc;
       obj[fname] = newFunc;
   };
   
   Aspects.restore = function(obj, fname) {
       obj[fname] = obj[fname].oldFunc;
   }
   
   // tracing function entry
   function traceEntry(args, oldFunc, thiz) {
       // print the name of the function
       print("entering " + oldFunc.name);
       // print arguments
       var str = "";
       for (var i = 0; i < args.length; i++) {
           str += args[i] + ", ";
       }
       print("arguments " + str);
       // return argument array - used by oldFunc.
       return args;
   }
   
   

   With the above code in a debug library (say "debug.js"), the client code can write something like:

   function add(x, y) { return x + y; }
   
   // just add two arguments
   add(3, 4);
   
   Aspect.addBefore(this, "add", traceEntry);
   // call add -- prints debug output on entry
   add(3, 4);
   
   // restore old "add" function without debug output
   Aspect.restore(this, "add");
   
   

6. Tracking global variables: It is better to avoid globals as much as possible.

   Use objects instead. It is easy to accidentally create globals in JavaScript. For example,

   
   
   function f() {
      x = m(); // forgot 'var' before x, x is global!
      // rest of the code...
   }
   
   
   

   While it may be possible to spot "unwanted" globals by code inspection, we can do better than that. It is possible to check global variable assignments and accesses using javax.script.Bindings used for global variable storage.

   
   import javax.script.*;
   import java.io.*;
   
   public class Test {
       public static void main(String[] args) throws Exception {
           // create a new ScriptEngineManager
           ScriptEngineManager m = new ScriptEngineManager();
           // get JavaScript engine instance
           ScriptEngine jsEngine = m.getEngineByName("javascript");
           // set a "debug" bindings for global variables
           jsEngine.setBindings(new DebugBindings(),  ScriptContext.ENGINE_SCOPE);
           // eval code from a java.io.Reader object.
           jsEngine.eval(new FileReader(args[0]));
       }
   }
   
   

   The DebugBindings class could look like

   
   
   // a simple Bindings implementation that prints debug output
   // whenever a variable is accessed or assigned.
   import javax.script.*;
   
   public class DebugBindings extends SimpleBindings {
     @Override public Object put(String name, Object value) {
         Object res = super.put(name, value);
         System.out.println("Global assign: " + name);
         return res;
     }
   
     @Override public Object get(Object key) {
         Object res = super.get(key);
         System.out.println("Global access: " + key);
         return res;
     }
   }
   
   

   When running the Test class with the following t.js script file,

   function h() {
      // global variable assign
      x = 32;
   }
   
   h();
   

   we get the following output..

   Global assign: context
   Global assign: print
   Global assign: println
   Global access: javax.script.filename
   Global assign: h
   Global access: h
   Global assign: x
   

   Note that debug output is printed for function "assignments" as well. Note that global functions are global variables with "function" value.

7. Debugging JavaScript objects

   Because JavaScript is dynamically typed language, we can replace an object with any other object that "looks" like the "original". i.e., the replacement objects should just support same methods, properties -- but can do anything. (If it walks like a duck and quacks like a duck, it must be a duck). You can wrap actual object with a "debuggable" object (whose methods print debug/trace output) -- so long as debug wrapper objects supports same methods, properties. Usually, it is very easy to wrap an object with another object in JavaScript. But, if your object supports properties (a.k.a fields) it becomes tricky to wrap the same - for example, you may want to wrap XMLHttpRequest that has properties. But, you can use JSAdapter and "hook" all property or method access or assignments.

What's New In WSH 5.6

Several areas of functionality have been addressed in this latest version of the Windows Script Host (version 5.6). Comparison table that lest features added to the new version can be found at WSH Version Information

Setting up Remote WSH

Remote WSH, which is a new technology included in WSH 5.6, provides the ability to run a script on a remote machine or machines. With Remote WSH, the script is physically copied from the local machine to the remote machine before executing. In order to enable Remote WSH functionality, you must first set up the remote machine with the proper security settings. The steps below perform the tasks that enable Remote WSH.

Ajax (programming) - Wikipedia, the free encyclopedia

Asynchronous JavaScript And XML, or its acronym Ajax, is a Web development technique for creating interactive web applications. The intent is to shift a great deal of interaction to the Web surfer's computer, exchanging data with the server behind the scenes, so that the entire Web page does not have to be reloaded each time the user makes a change. This is meant to increase the Web page's interactivity, speed, and usability. The Ajax technique uses a combination of:

• XHTML (or HTML) and CSS for marking up and styling information.
• The DOM accessed with a client-side scripting language, especially ECMAScript implementations like JavaScript and JScript, to dynamically display and interact with the information presented
• The XMLHttpRequest object to exchange data asynchronously with the web server. In some Ajax frameworks and in some situations, an IFrame object is used instead of the XMLHttpRequest object to exchange data with the web server.
• XML is commonly used as the format for transfering data, although any format will work, including preformatted HTML, plain text, JSON and even EBML.

Like DHTML, LAMP, or SPA, Ajax is not a technology in itself, but a term that refers to the use of a group of technologies together. In fact, derivative/composite technologies based substantially upon Ajax, such as AFLAX, are already appearing

Wise ASP - JScript Regular Expressions

One of the most overlooked features of JScript is the regular expression interpreter, which makes string pattern matching easy. Input validation is one of the most common requirements in Web site development. At design time, you don't know what exact values viewers will enter, but you do know the format they need to use. A regular expression is a way of representing a pattern you are looking for in a string.

Fabulous Adventures In Coding Are JScript strings passed by reference

Yesterday I asked "are JScript strings passed by reference (like JScript objects) or by value (like JScript numbers)?"

Trick question! It doesn't matter, because you can't change a string. I mean, suppose they were passed by reference -- how would you know? You can't have two variables refer to the "same" string and then change that string. Strings in JScript are like numbers -- immutable primitive values.

Of course, "under the covers" we actually have to pass the strings somehow. Generally speaking, strings are passed by reference where possible, as it is much cheaper in both time and memory to pass a pointer to a string than to make a copy, pass the value, and then destroy the copy.

John said:

Ok, first off, my little experience with JScript tells me that they are passed by reference. But, the comment above about it "doesn't matter" is complete BS. It matters quite a bit. Say you have an array of objects, and you want to fill the objects with data from a database. Say they contain mostly strings. Try this. Query your database, get a recordset, and set the strings in the object, to those returned by the record set. When you get done, all your objects will have null strings. Why? Because the strings were passed by reference, and the moveNext method on a record set does change the string values!

May 31, 2004 8:57 AM

Eric Lippert said:

I suspect that you're confusing two different usages of the term "by reference". When I asked whether JScript strings were passed by reference, I meant whether the STRING ITSELF was passed by ref or by value. You're talking about whether the MEMORY ADDRESS that holds the string is passed by value or by reference, which is a subtly different thing.

JScript passes objects by reference and numbers by value, but doesn't support passing references to variables at all.

Confused? It's a confusing topic. I wrote an article about the difference here:

http://blogs.msdn.com/ericlippert/archive/2003/09/15/53005.aspx

New in JavaScript 1.6 - MDC

ECMAScript for XML (E4X) is a powerful technology for creating and processing XML content within JavaScript. We're going to continue to improve our E4X support, including adding transparent integration with the existing DOM, but developers who are building XML-based web applications can benefit from E4X support in Firefox 1.5.

You can still use the standard MIME type when using E4X:

<script type="text/javascript">

However, E4X syntax may conflict with the common practice of putting scripts into HTML comments (<!--...-->) to hide them from old browsers. E4X may also conflict with the more modern practice of putting scripts within XML CDATA sections (<[CDATA[...]]>) to allow the symbols "<" and ">" in the script (note that this does not apply to HTML). If you see inexplicable syntax errors, add "; e4x=1" to the MIME type:

<script type="text/javascript; e4x=1">

Note that scripts in extensions always treat HTML comments as E4X literals. That is, the "e4x=1" is implicit.

Array extras

There are seven new Array methods that can be separated into two categories, item location methods and iterative methods. The item location methods are:

• indexOf() - returns the index of the given item's first occurrence.

• lastIndexOf() - returns the index of the given item's last occurrence.

The iterative methods are:

• every() - runs a function on every item in the array and returns true if the function returns true for every item.

• filter() - runs a function on every item in the array and returns an array of all items for which the function returns true.

• forEach() - runs a function on every item in the array.

• map() - runs a function on every item in the array and returns the results in an array.

• some() - runs a function on every item in the array and returns true if the function returns true for any one item.

For more information, see Nicholas C. Zakas' article, Mozilla's New Array Methods.

Array and String generics

Sometimes you would like to apply array methods to strings, these treat a string as an array of characters. E.g. in order to check that every character in the variable str is a letter, you would write:

function isLetter(character) {
  return (character >= "a" && character <= "z");
}

if (Array.prototype.every.call(str, isLetter))
  alert("The string '" + str + "' contains only letters!");

This notation is rather wasteful and JavaScript 1.6 introduces a generic shorthand:

if (Array.every(str, isLetter))
  alert("The string '" + str + "' contains only letters!");

Similarly you can easily apply String methods to any object:

var num = 15;
alert(String.replace(num, /5/, '2'));

developerWorks Linux Open source projects Web architecture SashXB lends mini-RAD to Linux

SashXB extends JavaScript with objects that wrap native functionality -- and provides all the necessary tools for writing applications from scratch. In this article, the developers of SashXB explore its inner workings and demonstrate how SashXB simplifies the development, download, and installation of applications.

While SashXB is not appropriate for all software projects, it is perfect for small- to medium-sized network client applications. Targeted at Web developers with HTML and JavaScript skills who want to write full-featured native applications, as well as experienced programmers who'd appreciate the convenience of rapid application development, SashXB is an open source application environment that exposes native functionality to JavaScript. It speeds the development process by encapsulating system calls, existing libraries, and other code in easily accessible "extensions," which are accessible as JavaScript objects. Low-level details are hidden from application developers, who only need to learn APIs for the new objects.

After briefly sketching out the SashXB architecture and detailing some of its important components, we will look at several applications and step through some sample code.

SashXB architecture
At its heart, SashXB consists of a runtime, locations, and extensions -- all of which are XPCOM components. Similar to Microsoft COM for Windows, XPCOM is a component system developed and used extensively by the Mozilla team that allows you to construct reusable modules. Unlike MS COM, XPCOM is cross-platform. Interfaces are defined by IDL files and can be implemented in and accessed from any language with proper bindings, which currently include C++, Python, Perl, and the Java language. All of our objects are implemented in C++.

Currently SashXB supports a wide variety of extensions. Core and Linux are always installed by default.

• Core: Consists of six sub-parts:
  • Channels: communicate with other Web applications
  • Cursor: manipulate the cursor
  • Process: start and kill processes
  • UI: show basic UI input boxes
  • Net: open HTTP connections (wraps Mozilla's HTTP transfer objects)
  • Platform: find information about the system you're running on
• Linux: show Linux-specific UI input boxes
• Registry: store and retrieve values
• Filesystem: manage files and folders
• GTK: manipulate GUI elements (wraps GTK)
• Glade: use Glade GUIs (wraps Glade)
• Comm: use network sockets
• FTP: access remote files
• Jabber: send instant messages (wraps Jabberoo)
• XML: parse XML documents (wraps Gdome)
• Vorbis: play Ogg Vorbis sound files (wraps Ogg Vorbis)
• LDAP: access LDAP databases (wraps OpenLDAP)
• MySQL: access MySQL databases (wraps MySQL)

Hierarchical Menus with the Underrated style.display Object

You can better manage your Web real estate using hierarchical menus. Learn how with these JavaScript examples by Bill Pena, coauthor of Designing with JavaScript, 2nd Edition.

You can embed JavaScript-script engine in your C applications By David Wall

You may have been pleased to welcome Microsoft's release of the Windows Script Engine (WSE), which was initially part of the Windows NT 4.0 Option Pack and has been available for use on business operating systems since then. The WSE opens certain aspects of Windows to manipulation via the JScript scripting language, which is very much like JavaScript in many ways. The company added a bunch of objects to represent Windows features, as well.

This was cool, but the greater significance (in my humble opinion) is that Microsoft had made a move toward making JavaScript-like languages the norm for application scripting. Rather than have a whole sheaf of application-specific languages, the move promised to make it easier for us to capitalize on our knowledge of JavaScript for all kinds of fun work.

Netscape saw this as good news as well, and has released the JavaScript API as a C library that may be incorporated, via a header file, in any C application you're writing. In other words, they've put out a file -- a DLL on Windows and a shared library for Unix -- that you can compile into your C applications. You can therefore send whole scripts to the JavaScript engine for processing (it, in effect, instantiates a JavaScript parser instance like the one that's running when your browser is operating). The engine supports scripts that are in compliance with ECMA-262, and with Netscape's JavaScript 1.4 specification.

Best of all, Netscape's C Engine for JavaScript requires no licensing fee. Consider it if you need a user-scriptable application.

Netscape's introductory document on the JavaScript C Engine: http://itw.itworld.com/GoNow/a14724a53277a75978418a3

Flash ActionScript -- An Introduction

When Macromedia released version 5 of Flash, one of the major changes was to their scripting language called ActionScript. Version 5 of ActionScript adopts the syntax and many of the built-in objects of JavaScript. Indeed, the developers used the ECMA standards for ECMAScript as their model for the upgrade. This article introduces some of the features of ActionScript and Flash, and describes the differences, advantages, and disadvantages of using Flash over competing technologies.

The Language

The syntax and basic language of ActionScript is largely identical to that of JavaScript. Some noticeable and specific differences include:

• Different document object models -- Because Flash works inside of it's own environment and is concerned with the elements like movies and sounds, it has a completely different object model. You won't find built-in objects like document and window.
• Not all JavaScript statements are supported -- There are a handful of statements that are not supported in ActionScript, including the switch statement and exception handling (try/catch/throw).
• ActionScript specific statements -- The language supports some non-JavaScript statements such as event handlers (e.g., onClipEvent) and message sending (e.g., tellTarget).
• Eval function -- The Eval function, in ActionScript, only evaluates variable references
• Built-in Objects -- ActionScript supports a subset of the built-in JavaScript objects such as Date and String and a subset of their methods and properties. For example, the String object lacks the standard regular expression functions such as search and replace.

Despite these differences, experienced JavaScript programmers will be comfortable with the language. Here is a code snippet from one of the example files:

function AddDigit(digit)
{
// Add a digit to the display
if (clear)
{
clear = false;
decimal = false;
display = "0";
}
if (display == "0" && digit != ".")
{
display = digit;
}
else
{
display = display + digit;
}
}

The larger learning challenge is understanding the overall environment and working with the new objects and capabilities provided.

ActionScript tutorial

ActionScript Dictionary

Flash ActionScript Course Outline

Details of the Document Object Model (DOM)
... reverse order of class-based languages ... JavaScript relates Manager to Employee as its ... JavaScript
terms inheritance would be ... containment in C++ and Java ...
www.prairienet.org/~sjmccaug/dom.htm - 47k - Cached - Similar pages

Server-Side JavaScript Guide
... Server-Side JavaScript ... members in C++, to be ... subclass of Employee that adds ... of the Manager
class would have ... JavaScript implements inheritance by allowing ...
docs.iplanet.com/docs/manuals/js/server/jsguide/obj2.htm - 56k - Cached - Similar pages

Website Abstraction General JavaScript Tutorials

Mar 18, 2000 FAQTS - Knowledge Base - View Entry - Is there an exception-error handling mechanism in core JavaScript by Martin Honnen, Thor Larholm

Netscape's JavaScript till version 1.3 (which is the version around in 
NN4 since NN4.06) has no error/exception handling mechanism in the core 
language. JavaScript 1.4 (which is only around in Netscape's server 
products) introduced
  try
  catch
exception handling and
  throw
exception throwing, JavaScript 1.5 which is (will be) around in NN6 
further added the 
  finally 
clause for try catch.
JScript 5 also supports
  try
  catch
  finally
and 
  throw
though the exception/error object differs between JavaScript and 
JScript (at least at the time of writing this, it is however expected 
that the final releases of JavaScript 1.5 and JScript 5.5 will be ECMA 
compliant).
Current inspection code of the form
  try {
    f();
  }
  catch (e) {
    var r = '';
    for (var p in e)
      r += p + ': ' + e[p] + '\n';
    alert(r);
  }
shows
  number: -2146823281
  description: object expected
with JScript 5 in IE and shows
  message: f is not defined
  name: ReferenceError
with JavaScript 1.5 in NN6. As the ECMAScript edition 3 standard 
prescribes
  message
and
  name
properties for
  Error
objects it seems that Netscape's JavaScript is already compliant with 
the standard in this regard while JScript has to catch up.

So how can we use that in client side JavaScript today? That is not 
easy at least in a cross browser way. For Netscape you can safely use 
JavaScript1.4/1.5 SCRIPT blocks e.g.
  <SCRIPT LANGUAGE="JavaScript1.4">
  try { ... } catch (e) { ... }
  </SCRIPT>
and
  <SCRIPT LANGUAGE="JavaScript1.5">
  try { ... } catch (e) { ... }
  </SCRIPT>
which NN6 will execute correctly while NN4 and earlier ignore these.
Unfortunately IE4/5 even with a JScript 5 scripting engine (which 
supports the try/catch statement) ignores JavaScript1.4/1.5 SCRIPT 
blocks. There seems to be no way to version a SCRIPT block for 
IE/JScript so that try/catch is executed in those browsers which 
support it and ignored otherwise.
However, in an IE 4/5 only environment, such as when client data is 
seperated serverside for different browsers, you can use
if (window.screenTop){
  try { ... } cath(e) { ... }
} else {
  ...
}

"Komodo will provide JavaScript developers with a robust, fully-featured development environment, and adding Perl and Python support to Mozilla will add new power to the Mozilla development platform."

[Jan 28, 2000] DDJ EXTENDING JSCRIPT by Paul Butcher (content of the paper is available from DDJ CD only)

Paul extends Microsoft's JScript scripting engine by adding support for constructors and arrays. In the process, he presents JScriptTest, a program that displays a UI that lets you type and execute JScript source. Additional resources include jstest.txt (listings) and jstest.zip (source code).

[Jan 28, 2000] SCRIPTS FOR WINDOWS SCRIPTING HOST by John Goalby (content of the paper is available from DDJ CD only)

Microsoft's Windows Scripting Host (WSH) is a language-independent batch-processing language for Win32. John presents a number of self-contained scripts that are useful to software developers, not just systems administrators. Additional resources include wsh.txt (listings) and wsh.zip (source code).

[Jan 21, 2000] OLE Automation in JavaScript -- Imagine being able to access and control Window's applications (like Word, etc.) using JScript! The Doc shows you how. By Dr. Yehuda Shiran.

[June 7, 1999] Win32 Scripting..... Automate!

[June 7, 1999] Winscripter

[June 7, 1999] PC Magazine PC Tech (File Management via Windows Scripting) Page 1 of 6

Recommended Links

Softpanorama Recommended

Top articles

Sites

• ECMAScript - Wikipedia, the free encyclopedia

• **** Google Web Directory - Computers Programming Languages JavaScript

• **** MSDN Online Web Workshop

• Microsoft Scripting Technologies Official page for Microsoft JScript

  • JScript User's Guide Provides information about how to use JScript and includes a guide to regular expressions.
  • JScript Language Reference Explains the elements that comprise the JScript language.

• **** JavaScript Source Free JavaScripts, Tutorials, Example Code, Reference, Resources, And Help

• **** Cetus Links - JavaScript - ECMAScript See also Cetus Links JScript

• **** DHTML Lab Free Dynamic HTML Tutorials, DHTML Scripts, Programming, Tools, Code, and Examples - dhtmlab.com

• ABOUT.COM/Javascript tutorials, scripts, answers, and much more Javascript

• JavaScript Articles, Links, and Resources - WebDeveloper.com

• Focus on JavaScript - Home Page

• HotSyte- The JavaScript Resource
• Dev Edge Online
• Doc JavaScript
• JavaScript.com
• JavaScripts.com
• The JavaScript Source
• Uncanny Programming

• EarthWeb.com /Javascript

• JavaScript.com - The Definitive JavaScript Resource JavaScript Tutorials and Free Java Scripts

• DHTML Lab Free Dynamic HTML Tutorials, DHTML Scripts, Programming, Tools, Code, and Examples - dhtmlab.com

• Yahoo! JavaScript -- excellent resource

• JavaScripter.net - JavaScript FAQ, quizzes, games, and more

• WebCoder.com - Your home for JavaScript and Dynamic HTML on the Web.

• http://developer.netscape.com/docs/manuals/javascript.html -- old site of now defunct Netscape corporation

  • Core JavaScript 1.4 Guide

  • Core JavaScript 1,4 Reference

  • Microsoft Word self-extracting binary of Javascript standart

  • Excerpts from the JavaScript^TM Bible (3rd Edition)

  • Other JavaScript Resources

  • Getting Started with Netscape JavaScript Debugger

  • Signing Software with the Netscape Signing Tool 1.0

  • Programmming JavaScript 1.2 Event Handlers

  • Programmming JavaScript 1.2 Event Handlers

  • Component Developer's Kit (CDK)

• Javascript jankee

• Website Abstraction
• WebCoder.com - Your home for JavaScript and Dynamic HTML on the Web.
• Rolling Scrolling Status Surfers
• Roller- A JavaScript Coder
• Textual Abuse Page
• Danny Goodman's Javascript Pages
• The Javascript Planet

Tutorials

• Website Abstraction General JavaScript Tutorials -- links to tutorials
• JScript tutorial - part 1 Covers Jscript 5.5
• JScript reference
• Website Abstraction General JavaScript Tutorials
• JScript Tutorial
• Voodoo's Intro to JavaScript (see also Voodoo's Intro to JavaScript)
• Core JavaScript 1.4 Guide
• Client-Side JavaScript 1.3 Guide
• Excerpts from the JavaScript^TM Bible (3rd Edition)
• Webmonkey JavaScript Index
• JavaScript Tutorial for Programmers
• Beginners Guide to JavaScript
• Experiments in JavaScript
• JavaScript Tutorial ( http://www.cs.brown.edu/courses/bridge/1998/res/javascript/javascript-tutorial.html )
• Web Resources Tutorials The Primers Let's Learn JavaScript!

Quiz:

• JavaScript.com Quiz

Older e-books

• Que: SE USING JSCRIPT
• Author: Mark Reynolds
  Price: $49.99 US
  Publisher: Que
  ISBN: 078971079X
  Publication Date: 12/5/96
  Pages: 700
• Que: SE Using JavaScript

Articles

JScript tutorial - part 1

FAQTS - Knowledge Base - View Entry - How do I make every word in a string start with a capital letter

Introduction to Regular Expressions Microsoft guide to Jscript regular expressions

The information contained in these pages is intended to provide a introduction to regular expressions in general.

While an attempt has been made to make each topic stand on it's own, much of the information contained in these topics relies upon the understanding of a previously introduced feature or concept. Therefore, it's recommended that you peruse these topics sequentially for the best overall understanding of the material.

The Introduction to Regular Expressions consists of the following individuals topics:

• Regular Expressions
• Early Beginnings
• Uses for Regular Expressions
• Regular Expression Syntax
• Build a Regular Expression
• Order of Precedence
• Ordinary Characters
• Special Characters
• Non-Printable Characters
• Character Matching
• Quantifiers
• Anchors
• Alternation and Grouping
• Backreferences

Windows and Frame from JavaScript The Definitive Guide, 3rd Edition

JavaScript Guidelines and Best Practice

NavWorks- Javascript Introduction

JavaScript Objects and Operators

Javascript Pages

FAQs

• JavaScript Guidelines and Best Practice

• Netscape DevEdge Online FAQ - Visual JavaScript

Reference

• Microsoft Windows Script 5.6 Documentation
  This download provides extensive reference and conceptual documentation for all of Microsoft Windows Script Technologies.

• Ecma WEB SITE

• ECMA-262 JavaScript Language Specification

  • Viewable, downloadable, and printable as a PDF file ECMA-262.pdf
  • Microsoft Word self-extracting binary

• Netscape (Documentation JavaScript)

  • Core JavaScript 1,4 Reference

  • Client-Side JavaScript Guide

  • Client-Side JavaScript Reference

  • 
    

• JavaScript FAQ by Alexei Kourbatov

• Object Hierarchy in IE

• DevEdge Online - Online JavaScript Reference Manual

• Microsoft Word self-extracting binary of Javascript standart

• A free copy of the JavaScript Object Roadmap and Quick Reference. The final version from the book is now available here (cover date: 2 January 1998). It is a .pdf (Adobe Acrobat) file that prints out on both sides of two pieces of paper and folds into a convenient reference. The new version shows Navigator and Internet Explorer compatibility ratings for every Netscape Navigator object and its properties, methods, and event handlers. I use it all the time.
  If you have the Acrobat reader plug-in, you can preview the entire document. Or download your choice of a Windows zipped version or Macintosh binhex version. The download versions include step-by-step instructions for printing, assembling, and folding the pages into a handy pamphlet format.

Script collections

• Microsoft Script Repository
• Microsoft Misc. Code Samples
• The JM Web JavaScript collection
• d e v h e a d Resources ScriptLibrary
• The JavaScript Planet - Collection with 371 FREE examples!

JScript

Microsoft's JScript Page

**** Cetus Links JScript

JScript Tutorial

Visual Javascript

No longer supported. See Netscape Visual Javascript 1.0 End Of Life Statement.

Papers

• Lab Note Building Distributed Web Applications with Visual JavaScript (Web Techniques, Feb 1998)
• Using components to develop applications, an introduction to Visual JavaScript
• Levelling the Playing Field: Visual JavaScript

Books

• new:Server Scripts With Visual Javascript (Hands-On Web Development)
• Netscape Visual JavaScript for Dummies (Amazon Link)
• Official Netscape Visual JavaScript Book (Amazon Link)
• Server Scripts With Visual JavaScript (Hands-On Web Development) (Amazon Link)
• Teach Yourself Visual JavaScript in 21 Days, Professional Reference Edition (Amazon Link)

Debugging Articles

• Debugging JavaScript programs - JavaWorld July 1996
• CNET Builder.com - Web Programming - Readers Write Debugging JavaScript Debugging JavaScript - 9-14-99
• The JavaScript Source Debugging Guide
• JavaScript - Debugging
• JavaScript Debugging
• Laura Lemay's Web Workshop--JavaScript
  • Ch14. Debugging JavaScript Programs
• webreview.com - Debugging JavaScript
• JavaScript Debugging -- Overview of Debugging in Netscape 6. Referenced Documents:
  • NEW 'query-part' patch for Netscape JavaScript Debugger 1.1
  • Documents for JavaScript Debugger for NGT
  • Basic JSD architecture
  • An old proposal for a JavaScript Debugger in JavaScript for Mozilla
  • An old high-level laundry list of things that ought to be done
  • js/jsd/README
  • js/jsdj/README
  • js/jsdj/build/README
  • js/jsdj/classes/com/netscape/jsdebugging/ifcui/README
• Advanced JavaScript Debugging Technique By Danny Goodman -- nothing advanced but still might be useful
  
• Debugging JavaScript programs - JavaWorld July 1996 -- decent . Republished in The JavaScript Source: Debugging Guide
• JavaScript Programming: Debugging / WebDeveloper.com by Heidi Brumbaugh
• CNET Builder.com - Web Programming - Readers Write: Debugging
• JavaScript - Debugging -- weak
• JavaScript Debugging -- slides

Jscript Debugger

Microsoft Script Debugger is a debugging environment that extends any Microsoft ActiveX Scripting host application (for example, Internet Explorer or Internet Information Server).

• Run your server-side scripts one line at a time.
• Open a command window to monitor the value of variables, properties, or array elements, during the execution of your server-side scripts.
• Set pauses to suspend execution of your server-side scripts (using either the debugger or a script command) at a particular line of script.
• Trace procedures while running your server-side script.
• To add breakpoints to your scripts insert a debugger statement before a suspect line of script. For example, the following script includes a debugger statement that interrupts execution and automatically starts the Microsoft Script Debugger each time the script loops through a new value.

  for (var count = 1; count <= 10; count++)  {        
    var eventest = count%2;				     
    debugger						    //Sets breakpoint	
    if (eventest == 0) {
      response.write("Even value is " + count + "<br>")
    }
  }

Note: You can use the debugger to view scripts and locate bugs, but not to directly edit your scripts. To fix bugs, you must edit your script with an editing program, save your changes, and run the script again.

• Starting Script Debugger
• Script Debugger Documentation
• Frequently Asked Questions
• Windows Script Interfaces
• Windows Script Debugging Interfaces

Javascript Engines

The following is a list of JavaScript engines.

• SpiderMonkey - JavaScript engine used in Mozilla Gecko applications including Firefox.
• Rhino - one of several JavaScript engines from Mozilla Written in Java
• JavaScriptCore - derived from KJS for Safari
• KJS - for Konqueror
• Narcissus - JavaScript implemented in JavaScript, used on top of SpiderMonkey.
• NGS
• NJS - a successor of NGS

Outliners/ Contents Generators

• Inside Dynamic HTML - Outlining -- classic outliner.

• The Joust Outliner -- The Outline Navigation System in JavaScript

• An Outlined Document

• JavaScript FAQ\

• Hierarchical Table of Contents- HiTOC 1.3

• Using EZ Outliner

• JavasScript DHTML outliner by Marcelino Martins Folder-Tree

• Chapter 5 -- An Outlined Document

• JavaScript SE Chapter 20

• Tutorial 2 - How to use Collapsible Outlines in a Shared Border & Creating Outlines that are Collasped by Default -- Frontpage

• Expandable Outlines Cross-Browser
  http://webreference.com/dhtml/column12/

• This site addresses the problems but produces errors when you view the site so I don't know if they are coding correctly, and it does not address IE5...I don't understand this enough, but for those of you who can code you should be able to address the cross-browser issues and the indent problem...Please get in touch with me if you feel like making a tutorial so that we can all use it!

• The Joust Outliner

• The JavaScript Sourcebook

• ezoutline folder

• Danny Goodman's JavaScript Pages

• Outline Table of Contents

Cookies

See also

• Elara Webdirectory Javascript Tutorials Cookies

• WebKnowHow.Net JavaScript Cookies

• Cookie Central

Crispy JavaScript Cookies Introduction - Doc JavaScript

The Unofficial Cookie FAQ -- FAQ for anyone interested in learn about cookies.

The JavaScript Source Cookie Scripts -- a dozen or so examples

EchoEcho.Com - javascript tutorial - javascript cookies

JavaScript Cookies - JavaScript tutorial - ready to use ...

Webmonkey tutorial

• Cookies using JavaScript -- summary of the Webmonkey tutorial

Workshop 5 Javascript 2 and Cookies

bruce-hamilton.com - cookies tutorial

JCL's HTML & JavaScript Tutorial

Useful JavaScript - JavaScript Cookies

Cookies and JavaScript A how-to guide for reading and writing cookies in JavaScript.

Everything You Ever Wanted to Know About Cookies from Web Reference.com.

Webmaster's Bakery from Web Developer.com.

Examples and information about using cookies in shopping cart

• How to make cookies and shopping cart
• The JavaScript Source Cookie Scripts -- a dozen or so examples

Making Cookies With JavaScript Information for including JavaScript cookies into your web site, from Builder.com.

Random Findings

**** A JavaScript Web-Ring

Netscape debugger

Netscape bundled a decent debugger with Visual JavaScript, but the product was discontinued. If you spend some serious effort coding Javascript, do yourself a favor and get the full debugger for Netscape. Netscape's built-in console is OK for catching typos and similar clean-up stuff, but you'll pull your hair out using it if what you really need to do is trace through a function--for instance, one that's working, but it's just not working the way you want/expect it to. Download it from jsdebug

Netscape/Mozilla Javascript. You must have Netscape Communicator 4.02 or later installed to run the debugger.

• DevEdge Online Netscape JavaScript Debugger 1.1
• Getting Started with Netscape JavaScript Debugger Document last modified: 12/11/97.
• jsdebug.html
• View Source The Java Script Apostle - Advanced JavaScript Debugging Techniques
• JavaScript Debugging

ScriptEase Desktop

ScriptEaseWebServer Edition

The ScriptEase:WebServer Edition enables the Webmaster/Web site developer to quickly and easily create exciting and interactive Web sites that will generate more interest, attract more clients, and make the Internet/Intranet an extremely effective and important part of any organization's business strategy.

ScriptEase:WebServer Edition is the first Web scripting product with an IDE Debugger, allowing you to debug your scripts from the client while they are still on the server. The SE:WSE Arcade demonstrates the wide range of solutions provided by ScriptEase:WebServer Edition.

ScriptEase:WebServer Edition combines all of the existing CGI interfaces (including ISAPI, WinCGI, ACGI, and LCGI) into one common interface for uniform treatment of scripting across all servers. The interpreter handles all format processing, including hex character replacement and tag separation. ScriptEase:WSE makes it easy to build: forms that support electronic commerce, customer surveys, database queries, scheduling, games, and more.

ScriptEase Debugger

ScriptEaseWebServer Edition -- probably the best non-Microsoft environment

ScriptEase:WebServer Edition is the first Web scripting product with an IDE Debugger, allowing you to debug your scripts from the client while they are still on the server. The SE:WSE Arcade demonstrates the wide range of solutions provided by ScriptEase:WebServer Edition.

ScriptEase:WebServer Edition combines all of the existing CGI interfaces (including ISAPI, WinCGI, ACGI, and LCGI) into one common interface for uniform treatment of scripting across all servers. The interpreter handles all format processing, including hex character replacement and tag separation. ScriptEase:WSE makes it easy to build: forms that support electronic commerce, customer surveys, database queries, scheduling, games, and more.

Etc

Society

Groupthink : Two Party System as Polyarchy : Corruption of Regulators : Bureaucracies : Understanding Micromanagers and Control Freaks : Toxic Managers :   Harvard Mafia : Diplomatic Communication : Surviving a Bad Performance Review : Insufficient Retirement Funds as Immanent Problem of Neoliberal Regime : PseudoScience : Who Rules America : Neoliberalism  : The Iron Law of Oligarchy : Libertarian Philosophy

Quotes

War and Peace : Skeptical Finance : John Kenneth Galbraith :Talleyrand : Oscar Wilde : Otto Von Bismarck : Keynes : George Carlin : Skeptics : Propaganda  : SE quotes : Language Design and Programming Quotes : Random IT-related quotes :  Somerset Maugham : Marcus Aurelius : Kurt Vonnegut : Eric Hoffer : Winston Churchill : Napoleon Bonaparte : Ambrose Bierce :  Bernard Shaw : Mark Twain Quotes

Bulletin:

Vol 25, No.12 (December, 2013) Rational Fools vs. Efficient Crooks The efficient markets hypothesis : Political Skeptic Bulletin, 2013 : Unemployment Bulletin, 2010 :  Vol 23, No.10 (October, 2011) An observation about corporate security departments : Slightly Skeptical Euromaydan Chronicles, June 2014 : Greenspan legacy bulletin, 2008 : Vol 25, No.10 (October, 2013) Cryptolocker Trojan (Win32/Crilock.A) : Vol 25, No.08 (August, 2013) Cloud providers as intelligence collection hubs : Financial Humor Bulletin, 2010 : Inequality Bulletin, 2009 : Financial Humor Bulletin, 2008 : Copyleft Problems Bulletin, 2004 : Financial Humor Bulletin, 2011 : Energy Bulletin, 2010 : Malware Protection Bulletin, 2010 : Vol 26, No.1 (January, 2013) Object-Oriented Cult : Political Skeptic Bulletin, 2011 : Vol 23, No.11 (November, 2011) Softpanorama classification of sysadmin horror stories : Vol 25, No.05 (May, 2013) Corporate bullshit as a communication method  : Vol 25, No.06 (June, 2013) A Note on the Relationship of Brooks Law and Conway Law

History:

Fifty glorious years (1950-2000): the triumph of the US computer engineering : Donald Knuth : TAoCP and its Influence of Computer Science : Richard Stallman : Linus Torvalds  : Larry Wall  : John K. Ousterhout : CTSS : Multix OS Unix History : Unix shell history : VI editor : History of pipes concept : Solaris : MS DOS :  Programming Languages History : PL/1 : Simula 67 : C : History of GCC development :  Scripting Languages : Perl history   : OS History : Mail : DNS : SSH : CPU Instruction Sets : SPARC systems 1987-2006 : Norton Commander : Norton Utilities : Norton Ghost : Frontpage history : Malware Defense History : GNU Screen : OSS early history

Classic books:

The Peter Principle : Parkinson Law : 1984 : The Mythical Man-Month :  How to Solve It by George Polya : The Art of Computer Programming : The Elements of Programming Style : The Unix Hater�s Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite

Most popular humor pages:

Manifest of the Softpanorama IT Slacker Society : Ten Commandments of the IT Slackers Society : Computer Humor Collection : BSD Logo Story : The Cuckoo's Egg : IT Slang : C++ Humor : ARE YOU A BBS ADDICT? : The Perl Purity Test : Object oriented programmers of all nations : Financial Humor : Financial Humor Bulletin, 2008 : Financial Humor Bulletin, 2010 : The Most Comprehensive Collection of Editor-related Humor : Programming Language Humor : Goldman Sachs related humor : Greenspan humor : C Humor : Scripting Humor : Real Programmers Humor : Web Humor : GPL-related Humor : OFM Humor : Politically Incorrect Humor : IDS Humor : "Linux Sucks" Humor : Russian Musical Humor : Best Russian Programmer Humor : Microsoft plans to buy Catholic Church : Richard Stallman Related Humor : Admin Humor : Perl-related Humor : Linus Torvalds Related humor : PseudoScience Related Humor : Networking Humor : Shell Humor : Financial Humor Bulletin, 2011 : Financial Humor Bulletin, 2012 : Financial Humor Bulletin, 2013 : Java Humor : Software Engineering Humor : Sun Solaris Related Humor : Education Humor : IBM Humor : Assembler-related Humor : VIM Humor : Computer Viruses Humor : Bright tomorrow is rescheduled to a day after tomorrow : Classic Computer Humor

The Last but not Least Technology is dominated by two types of people: those who understand what they do not manage and those who manage what they do not understand ~Archibald Putt. Ph.D

The statements, views and opinions presented on this web page are those of the author (or referenced source) and are not endorsed by, nor do they necessarily reflect, the opinions of the Softpanorama society. We do not warrant the correctness of the information provided or its fitness for any purpose. The site uses AdSense so you need to be aware of Google privacy policy. You you do not want to be tracked by Google please disable Javascript for this site. This site is perfectly usable without Javascript.

Last modified: March 12, 2019