Datasheet

Chapter 1: What Is JavaScript?
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The numbering scheme is based on the idea that Firefox 4 will feature JavaScript 2.0, and each increment
in the version number prior to that point indicates how close the JavaScript implementation is to the 2.0
proposal. Though this was the original plan, it is unclear if Mozilla will continue along this path given
the popularity of the ECMAScript 3.1 proposal.
Summary
JavaScript is a scripting language designed to interact with web pages and is made up of the following
three distinct parts:
ECMAScript, which is defined in ECMA - 262 and provides the core functionality
The Document Object Model (DOM), which provides methods and interfaces for working with
the content of a web page
The Browser Object Model (BOM), which provides methods and interfaces for interacting with
the browser
There are varying levels of support for the three parts of JavaScript across the five major web browsers
(Internet Explorer, Firefox, Chrome, Safari, and Opera). Support for ECMAScript edition 3 is generally
good across all browsers, whereas support for the DOM varies widely. The BOM, the only part of
JavaScript that has no corresponding standard, can vary from browser to browser though there are some
commonalities that are assumed to be available.
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It ’ s important to note that only the Netscape/Mozilla browsers follow this versioning
scheme. Internet Explorer, for example, has different version numbers for JScript.
These JScript versions don ’ t correspond whatsoever to the JavaScript versions
mentioned in the preceding table. Further, most browsers talk about JavaScript
support in relation to their level of ECMAScript compliance and DOM support.
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