About javascript - AJAX

JavaScript was developed from a language called LiveScript, which was developed by Netscape for use in its early browsers. JavaScript source code is embedded within the HTML code of web pages and interpreted and executed by the browser when the page is displayed.

Using JavaScript, you can add extra functionality to your web pages. Examples include

  • Change the way page elements are displayed
  • Add animation and other image effects
  • Open pop-up windows and dialogs
  • Check the validity of user-entered data

Nearly all modern browsers support JavaScript, though with a few differences in some commands. Where these occur, they are described in the text.

Why Do I Need To Know About JavaScript?
The j in Ajax stands for JavaScript; you use functions written in this language and embedded within your web pages to formulate Ajax servercalls and to handle and process the response returned from the server.

What Is (and Isn’t) Covered in This topic
There is no room here for an exhaustive guide to all JavaScript’s functions. Instead this lesson concentrates on those aspects of the language necessary for later developing Ajax applications.

After completing this topic, you’ll have experience with the following:

  • Embedding JavaScript commands and external JavaScript files into web pages
  • Using some of the common JavaScript commands
  • Using event handlers to launch JavaScript commands
  • Working with JavaScript variables and objects
  • Abstracting JavaScript commands into functions

JavaScript Basics
JavaScript commands can be embedded directly into HTML pages by placing them between <script> …</script> tags. It is also common for JavaScript functions to be kept in a separate file on the server (usuallywith a file extension .js) and linked to HTML files where required, by placing a line like this into the head of the HTML file:

This allows you to call any JavaScript with in the file myJS.js, just as if that source code had been typed directly into your own web page.

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