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ECMAScript 5th Edition
I n December 2009, ECMA-262 5th Edition, commonly referred to as
ECMAScript 5, or simply ES5, was finalized and published by ECMA International.
This marked the first significant update to the core JavaScript language in 10 years.
ECMAScript 5 is the successor to ECMAScript 3, and is a mostly backwards com-
patible update of the language that codifies innovation by browser vendors over the
past decade and introduces a few new features.
ECMAScript 4 was never realized, and is part of the answer to why the language
could go without standardized updates for 10 years. This draft was widely considered
too revolutionary an update, and introduced several features that would not work
well with existing browsers. To this day, Adobe's ActionScript (used in Flash) and
Microsoft's JScript.Net are the only runtimes to implement a significant amount of
the proposed updates from ES4.
In this chapter we will take a cursory look at the most interesting changes in
ES5, and have a look at some of the programming patterns the new specification
enables. Particularly interesting are new additions to objects and properties, and
these will be afforded the bulk of our attention. Note that this chapter does not
cover all changes and additions in ECMAScript 5.
8.1 The Close Future of JavaScript
Backwards compatibility has been a major concern of ES5. JavaScript is
ubiquitous—every web browser released since the mid to late nineties supports
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