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Jscript Function Statement | How To Write Jscript Functions

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In order to create a JScript, you only need to open your text editor, create a plain text file, add a few JScript statements to it, and then save it with a .js file extension. For example, create a new JScript called my_first_prog.js and add the following statements to it.

//Script 1.5 - Your first JScript

WScript.Echo("Well To ProgrammingDost!");

The first statement is a comment that was embedded within the file to document the script's name and purpose. The second statement displays a text message. The composition of the second statement is as follows. First the WScript object is referenced. This object is different from the WScript execution host. Then a method called Echo, which belongs to the WScript object, is executed and passed the text string "Well To ProgrammingDost!". Don't worry if this all sounds a little confusing or overwhelming now. By the time that you get through Sunday evening, you'll understand how this stuff works. For now, just follow along and focus on the steps involved in creating and executing your first JScript.

When executed by either the WScript or CScript execution host, this JScript displays its message. However, depending on which execution host you choose to use when running the script, the results will vary significantly.

If you were to run the scripts directly from the Windows desktop by double-clicking on it, Windows would, by default, run it using the WScript execution host. As a result, the script's output would be displayed in the form of a graphical pop-up dialog.

NOTE

You can also use the WScript execution host to run scripts from the Windows command prompt,in which case the script will run exactly as if you had started it from the Windows desktop.

Even some of the most experienced computer users have limited experience working with the Windows command prompt and little if any understanding of the Windows commands that are available. However, if you plan on becoming a serious JScript programmer, you need to get comfortable working with the Windows shell.

The Windows shell provides a text-based interface between the user and the operating system. Instead of using the computer's mouse to point and click your way through the Windows graphical user interface, you work with the Windows shell by typing in text commands. The Windows shell translates these commands into a format the operating system can understand. Likewise, the Windows shell translates any output returned by the operating system into a format that people can understand.

You enter commands for the Windows shell to process by typing them in at the Windows command prompt. For example, on a computer running Windows XP, you would start up a new Windows shell session by clicking on Start, All Programs, Accessories, and then Command Prompt.

TIP

As a shortcut, you can start up a new Windows shell session and access the Windows command prompt by clicking on Start, Run, typing CMD, and then clicking on OK.

NOTE

If your script resides in a folder other than the folder upon which the Windows shell is currently focused, you must supply the complete path to the folder where the script is stored. For example, if your script were stored in C:\Jscripts, then you would need to use the following command to run it using the WScript execution host.

TIP

If you are faster at the keyboard than you are with your mouse then you can also close the Command Prompt windows by typing EXIT and pressing the Enter key.

Jscript Introduction | What is Jscript

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Jscript and VBScript are the two default scripting languages which are supplied by the Microsoft to use with the WSH (Windows Script Host). Both the languages are pretty much similar to each other. These are very useful when it comes to the automating small tasks.

NOTE

As you know that the VBScript is derived from Visual Basic programming language. Like JavaScript,VBScript can also be used for Web page development. However, while Internet Explorer supports VBScript, it does not work with some browsers like in past with Netscape. This makes VBScript a less universally accepted scripting language. In addition, VBScript is proprietary. This means that Microsoft owns it, whereas the current version of JavaScript and JScript are based on the ECMAScript standards, so no one company controls its future. As a result, many people prefer JavaScript and JScript to VBScript.

There are some easy function in Jscript and JavaScript to solve complex calculations. But you will find a better way in VBScript to work with the arrays. People with a JavaScript background will be able to put together the move to JScript with very little effort. Similarly, people with a strong Visual Basic programming background may prefer learning VBScript. Some other third-party scripting languages are available that also can be used with the WSH. These languages include PERL, Python and REXX.

The main reason for using JScript and the WSH (Windows Script Host) is to save you time by automating system tasks. At the heart of every one of Microsoft's Windows operating systems is an intuitive graphical user interface (GUI). This GUI is designed to make the computer easy to use. All that you have to do is grab on to the mouse and point and click your way around.

Unfortunately, the GUI is not well suited to many tasks, particularly those that are highly repetitious or that involve many steps. For example, suppose that you are responsible for defining new user accounts on a shared computer in your department at work, and one day your boss comes in with a floppy disk containing a file with a list of 100 newly hired employees.

Using the GUI, you'd probably spend hours in front of the computer defining new user accounts, during which time no one else could use the computer to get any work done. On the other hand, you could write JScript and use the WSH to run it in less than an hour. This script could even be designed to read the file provided by your boss and to create a new user account for each name stored in the list. Once executed, the script would create the new user accounts within seconds. Best of all, once it is written, you could return and run the script again in the future with no additional work on your part to create new user accounts.

What Is Wsh | What Is Windows Script Host

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The WSH is an optional software element that supports the execution of scripts on Windows operating systems. It is tightly coupled with the operating system, meaning that it provides direct access to a number of Windows resources, including these:

Ø  The Windows desktop and Start menu

Ø  The Windows Quick Launch Bar

Ø  The Windows file system

Ø  Local and network printers and drives

Ø  Windows applications

Ø  Windows services

Ø  User accounts

Ø  The Windows registry

The WSH gives the most complete scripting environment available today for all Windows operating systems. When combined with a scripting language such as JScript, it provides a perfect platform for developing scripts that can automate virtually any Windows task.

Regardless of which of the Microsoft operating systems you own or support, you will want to make sure that you have upgraded the version of the WSH that is installed to the most current version. Microsoft provides access to the most current version of the WSH through its official scripting Web site, msdn.microsoft.com/scripting, where you can download WSH for free.

A Brief Overview of the WSH Architecture

The WSH provides built-in support for both JScript and VBScript. In addition, it can support any third-party, WSH-compatible scripting language, including PERL, Python, and REXX. In the future, third-party software developers may provide other WSH-compatible scripting languages. Microsoft designed the WSH to be very extensible, as evidenced by the number of third-party scripting languages that has already been set up to work with it. However, because JScript and VBScript are supplied with the WSH, they are the most commonly used scripting languages.

The WSH is a 32-bit application. Its architecture consists of three separate layers. First there are the various WSH-supported scripting engines. These scripting engines interpret script statements and pass them on to an execution host for processing.

The WSH provides two different execution hosts. The WScript execution host is designed to support the execution of scripts directly from the Windows desktop. The CScript execution host, on the other hand, is designed to support the execution of scripts from the Windows command prompt. Each of these execution hosts exists as a separate executable file named Wscript.exe and Cscript.exe, respectively.

With one exception, the WScript and CScript execution hosts provide the same level of functionality. This exception is the WScript execution host's capability to enable scripts to display text messages and collection input from users using graphical pop-up dialogs. This makes the WScript execution host the proper choice for scripts that need to interact directly with users. The CScript execution host, on the other hand, generally is used to run scripts that do not interact with users or to run scripts for users who are comfortable working from the Windows command prompt. However, the WScript execution host can be used to run scripts from the command line as well. Unless your script is designed to generate graphical pop-up dialogs, the choice of which script execution host to use is completely arbitrary.

The purpose of the WSH core object model is to provide access to Windows resources. It accomplishes this by defining objects that represent actual resources. These objects can then be accessed and manipulated by scripts, thus allowing the scripts to access and manipulate the resources that the objects represent. Examples of the types of objects that the WSH makes available include objects that represent Windows shortcuts, files, folders, and disk drives. The WSH also provides objects that represent network resources such as network drives and printers. On top of all this, the WSH object model also provides access to system resources such as Windows events logs and the Windows registry.

Every object that is presented by the WSH is associated with a collection of properties and methods. For example, a file is an example of an object. File objects have file names and file extensions. By accessing these file object properties, your JScripts can locate files that they want to work with. In addition, by modifying file object properties, your JScripts can rename files and change their file types.

Include Javascript File in Html

Ways of Embedding and Integrating JavaScript in the HTML Pages

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As you know, there are two places you can put your JavaScripts in an HTML page: in either the head or body section. In addition, I have told you that you can either embed JavaScript directly into the HTML page or reference it in as an external .js file. One more way you can integrate JavaScript into an HTML page is as a component in an HTML tag.

As we already told you that we can put our JavaScript code in anywhere in <head> or in <body> tags. We told you that you can embed your code directly or in your code or by saving it in another file and then referring the web page to get data from that external file. Here we are going to define how to use both ways of embedding code in an HTML page.

Using or Embedding JavaScript Code in the Body Section of an HTML page

JavaScripts embedded with the <SCRIPT> and </SCRIPT> tags can be placed anywhere in the body section of an HTML page. Scripts embedded in the body section are executed as part of the HTML document when the page loads. This enables the script to begin executing automatically as the page loads. For example, the statements shown below demonstrate how to embed a JavaScript within the body section of an HTML page.

<BODY>

  <SCRIPT TYPE="Text/JavaScript" LANGUAGE="JavaScript" >

    document.write("Code embedded in the body of an HTML page.");

  </SCRIPT>

</BODY>

JavaScript can be used or embedded more than once in the HTML pages.

<BODY>

  <SCRIPT TYPE="Text/JavaScript" LANGUAGE="JavaScript" >

    document.write("First embedded code in the body section.");

  </SCRIPT>

  <BR>

  <SCRIPT LANGUAGE="JavaScript" TYPE="Text/JavaScript">

    document.write("Second embedded code in the body section.");

  </SCRIPT>

</BODY>

Embedding the JavaScript in <Head> and </Head> tags in HTML pages

JavaScripts can also be placed anywhere within the head section of your HTML pages. Unlike scripts embedded within the body section of HTML pages, scripts embedded in the head section are not necessarily automatically executed when the page loads. In some cases, they are executed only when called for execution by other statements within the HTML page. Most JavaScript programmers move all functions and most variables to the head section because this ensures that they will be defined before being referenced by scripts located in the body section of the page.

NOTE

Variables are containers for storing information in computer memory. Functions are groups of JavaScript statements that you can call to perform a specific task. We'll talk more about the benefits of using functions and variables in upcoming posts.

The following statements show an HTML page with a JavaScript embedded in the head section. This script will automatically execute when the HTML page is loaded.

<HTML>

  <HEAD>

    <TITLE>Programming Dost Home Page</TITLE>

    <SCRIPT TYPE="Text/JavaScript" LANGUAGE="JavaScript">

      window.alert("JavaScript is executing from the Head section");

    </SCRIPT>

  </HEAD>

  <BODY>

  </BODY>

<HTML>

Using JavaScript with an External file in HTML pages

To store your JavaScripts in external files, you need to save them as plain text files with a .js file extension. You then need to add the SCR attribute to the opening <SCRIPT> tag in your HTML page as stated here.

<SCRIPT SRC="myExternalFile.js" TYPE="Text/JavaScript" LANGUAGE="JavaScript" > </SCRIPT>

In this example, an external JavaScript named myExternalFile.js has been used. This external JavaScript can contain any number of JavaScript statements or code. However, it cannot have any HTML whatsoever. Otherwise you'll end up with an error. For instance, the contents of the myExternalFile.js script  might be very simple as follows:

document.write("External JavaScript for the friends(dost) of Programming Dost.");

There are many advantages to putting JavaScripts in externally referenced files. For beginners, by getting JavaScripts out of your HTML pages you make your HTML pages smaller and easier to work with. In addition, you can reuse the JavaScripts stored as external files over and over again by referencing them from any number of HTML pages. This way if you create a script that you want to reference from several HTML pages, you can do so without having to insert the same script in all HTML pages over and over again. As a plus, should you ever want to alter the functionality of an externally stored script, you can do it by changing the code in the external file and all is done for you.

NOTE

There is no limit of the external file which can be called in an HTML page. And there is not limit of code use in the external file.

Use of JavaScript in the HTML tags in Web Pages

JavaScript can also be placed within HTML tags, as shown in the following example.

<BODY onLoad=document.write("Hello World! From Programming Dost")> </BODY>

In this example, the JavaScript onLoad=document.write("Hello World! From Programming Dost ") statement has been added to the HTML <BODY> tag. This particular JavaScript statement tells the browser to write the enclosed text when the browser first loads the HTML page.

JavaScript and Case Sensitivity | JavaScript Case Sensitivity

JavaScript and Case Sensitivity

It should be kept in mind the JavaScript is a case sensitive programming language (Not like the HTML). So you should be extremely careful about the code you embed while using JavaScript. Case sensitivity means that you must type JavaScript elements exactly as they appear in this book in order for them to work. For example, as far as JavaScript is concerned, the words “variable” and “Variable” refer to two different things, so pay special attention when typing your scripts. As for example in our program instead of using document.write() we mistaken and used Document.write() so our program ended with an error. So be very careful with JavaScript’s case sensitivity.

Insert JavascriptInto Html

Integrating JavaScript with HTML

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JavaScript is a collection of some or many programming statements that a programmer embeds in an HTML document. These statements will work or affect the HTML when they are placed in the <script> and </script> tags. Placement of these tags is up to the developer that where he or she wants to put them in the head section or in the body section.

Previously the Language was used to specify the type of the <script> tag. For example:

<script LANGUAGE="JavaScript1.5" > </script>

According to the HTML 4.0 specification, the TYPE attribute is now the proper way to go. However, you can continue to use both attributes if you want, in order to ensure that older browsers don't get confused. When working with JavaScripts, the TYPE attribute will always be Text/JavaScript.

Another way to work with JavaScripts is to store them in external files that have a .js file extension and then to reference those files from within your HTML pages. To accomplish this, you use the SRC attribute to specify the location of an external JavaScript file.  This is use full as it makes difficult for the user to view the JavaScript code.  It also makes it possible to share the same JavaScripts among multiple HTML pages. Once you have defined the opening and closing tags, you can begin placing JavaScript statements between them.

Before writing your first program in JavaScript you should know a little about the structure of the HTML page. If you are not so familiar with these tags and structure please do check the Programming Dost’s Learning HTML section.

<HTML>

  <HEAD>

    <TITLE>The Title of the Page goes here</TITLE>

  </HEAD>

  <BODY>

  </BODY>

</HTML>

This HTML page structure contains the <HEAD> </HEAD>, <TITLE> </TITLE>, and <BODY> </BODY> tag sets all wrapped inside the starting and ending <HTML> </HTML> tag set. If you want to do so, create your own template now. When you are done, add the following lines inside the body section:

<SCRIPT TYPE="Text/JavaScript" LANGUAGE="JavaScript" >

  document.write("Hello World From Programming Dost");

</SCRIPT>

After you put the code in the head or body tags the code will look like:

<HTML>

  <HEAD>

    <TITLE> The Title of the Page goes here</TITLE>

  </HEAD>

  <BODY>

    <SCRIPT TYPE="Text/JavaScript" LANGUAGE="JavaScript" >

      document.write("Hello World From Programming Dost");

   </SCRIPT>

  </BODY>

</HTML>

How to test your JavaScript Code?

Now that you have typed in your first script, you need to save it. We called this script as javaScriptTutorial_1.html. The HTML extension identifies the page as an HTML page. Your computer uses the information in the file's extension to associate the file with a particular application. An .html extension tells the operating system to open its default browser and pass the HTML file to it. Alternatively, you can use the .htm extension, which is also recognized as an extension for HTML pages.

If you are using a full-featured HTML editor, the editor may enable you to test your script with the click of a button like Dreamweaver or Visual Studio etc. Because Notepad has no such automatic HTML testing feature, we simply started up a browser and used it to open the javaScriptTutorial_1.html file. The browser opened our page and ran the script.