Professional JavaScript for Web Developers, 4th Edition

1What Is JavaScript?

WHAT'S IN THIS CHAPTER?

• Review of JavaScript history
• What JavaScript is
• How JavaScript and ECMAScript are related
• The different versions of JavaScript

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Please note that all the code examples for this chapter are available as a part of this chapter's code download on the book's website at www.wrox.com/go/projavascript4e on the Download Code tab.

When JavaScript first appeared in 1995, its main purpose was to handle some of the input validation that had previously been left to server-side languages such as Perl. Prior to that time, a round-trip to the server was needed to determine if a required field had been left blank or an entered value was invalid. Netscape Navigator sought to change that with the introduction of JavaScript. The capability to handle some basic validation on the client was an exciting new feature at a time when use of telephone modems was widespread. The associated slow speeds turned every trip to the server into an exercise in patience.

Since that time, JavaScript has grown into an important feature of every major web browser on the market. No longer bound to simple data validation, JavaScript now interacts with nearly all aspects of the browser window and its contents. JavaScript is recognized as a full programming language, capable of complex calculations and interactions, including closures, anonymous (lambda) functions, and even metaprogramming. JavaScript has become such an important part of ...