ECMAScript Support Matrix

There Is No Javascript

Copyright © 2005–2012 Thomas Lahn <js@PointedEars.de> (contributors)

Available online at http://PointedEars.de/scripts/test/es-matrix/

Table of contents

• Foreword and rationale
• Language features
• Version information
  • Netscape/Mozilla.org JavaScript
  • Microsoft JScript
  • Google V8
  • Apple JavaScriptCore
  • Opera ECMAScript
  • Adobe ActionScript
  • ECMAScript compatibility
• List of contributors

Foreword and Rationale

Many people talk about JavaScript as if it was a fully specified and universally implemented programming language. But that is in fact only the name of one implementation (at the time of writing, not even the widest distributed one) of a standard for an extensible programming language, ECMAScript, which is enjoying several implementations that are widely distributed (primarily, but not solely, through web browsers). This common misconception reaches so far as some rather knowledgable people – out of lazyness or ignorance – choose to refer to this pseudo-language using an alternate capitalization, like “Javascript” or “javascript” in an attempt to distinguish it from the original, JavaScript™ (an example of this can still be seen in the comp.lang.javascript FAQ). This is rather unsurprising since JavaScript is, as Douglas Crockford put it so aptly, the world's most misunderstood programming language.

However, either terminology is misleading; both should first be deprecated, and eventually abolished. The former kind, because it simply misses the point: for example, JavaScript is not JScript. The latter kind, because it is oversimplifying the issue, thereby shadowing the problems that are likely to occur if script code is not written with the existence of different implementations in mind. It is also potentially ambiguous, and leads to odd notation in English and other languages (like "javascript" at the beginning of a sentence, where it should be capitalized by convention, or in the midst of a sentence where it should be capitalized as well because it is a proper noun, after all). Such oversimplifying talk from supposed experts is potentially and evidentially harmful, not only for the experts themselves, but also for the beginners which are mislead and confused by this. It is a Bad Idea™ to keep people in the dark!

In order to achieve greater understanding of this topic, it is important to realize the similarities and the differences between implementations, the advantages and the bugs of each implementation. Differences are pointed out best using different words, not similar ones. For an analogy, you would never call a cat a dog just because both are implementations of the concept “animal” and both are equipped with a tail. Yet this describes exactly what often happens when people are discussing ECMAScript-based script programming: for example, they say “JavaScript” (any capitalization) and mean, often without providing that context information, ECMAScript-based scripting in IE or IIS, that is, Microsoft JScript instead! Who is to tell how the script must look like that they are talking about without further inquiry, then?

Therefore, for lack of a better alternative, the precise and equally concise term ECMAScript implementation(s) should be used when talking about features that several implementations (ought to) have in common (per the ECMAScript Language Specification). And whenever it was talked about one particular implementation, its proper name should be used, like Netscape/Mozilla.org JavaScript or simply JavaScript (if there is doubt, "™" might be added to emphasize that the implementation is meant). In all other instances, the term “JavaScript” (any capitalization) should not be used.

This overview began as a comparison of different “JavaScript” features and, as time passed and understanding grew, evolved into a comparison between the major ECMAScript implementations, detailing the differences, the quirks and the bugs. It has served its author (and its dedicated readers) for years in writing client-side scripts that work cross-browser, and helped to see the distinction between core language features, and APIs with language binding, like the DOM. (The features of the latter API will be compared in another Matrix.)

Whenever you read from this author that key line from arguably the most groundbreaking hacker movie ―“The Matrix has you!”― a suggestion is being considered as a contribution to this overview. See below.

Language Features

The following table lists all features of ECMAScript implementations that are not part of the first versions/editions of all of these languages, with the version/edition that introduced it; furthermore, information about features that have been deprecated is included. That means if a language feature is not listed here, you can consider it to be universally supported.

In addition, features have been highlighted with a greenish background color if this author considers them safe to use without prior feature test even when they do not appear to be formally specified or to be supported among all versions of all implementations considered here. This is based on the fact that all minimum versions of the implementations that a feature requires can be considered obsolete because the user agents known to implement them can be considered obsolete (see the respective version information for details). Note that this assessment is likely to be subject to change as more implementations are evaluated. If taken as a recommendation for design decisions, it should be taken as a light one.

The content of this table is based on what could be found in vendor's online documentations to date and on occasions where the respective features could be tested; it does not claim to be accurate or complete (please note how each feature is marked). Any correction/addition as to how things really are is welcome and will be credited where it is due.

Known Display Problems

• Firefox 3.0.x: If the scrollable table body flows out of the table, you are observing Bug 423823, fixed since Firefox 3.0.2. The Firefox 3.0 branch has met its end-of-life on 2010-03-30 CE. If you are still using Firefox 3.0.x as your primary browser, you are strongly recommended to update Firefox (but see below). As an alternative, you can toggle table body scrollability.
• Firefox 4.0+: The support for scrollable table body has been removed per Bug 28800. This violates the CSS3 Basic Box Model specification, which is only a Working Draft at the time of writing but is intended to replace the corresponding parts of CSS 2.1. If you want this useful feature (back), please comment on and vote for Bug 67421.

Since both of these were regressions, this author deems it necessary not to cover any of them with a workaround.

Version Information

• Netscape/Mozilla.org JavaScript
• Microsoft JScript
• Google V8
• Apple JavaScriptCore
• Opera ECMAScript
• Adobe ActionScript
• ECMAScript compatibility
• Timeline

Netscape/Mozilla.org JavaScript Version Information¹⁾

Microsoft JScript Version Information²⁾

Google V8 Version Information

Apple JavaScriptCore Version Information

Opera ECMAScript Version Information

Macromedia/Adobe ActionScript Versions³⁾

ECMAScript Compatibility

The following table provides a rough overview of ECMAScript Editions and relations between them and versions of their implementations. Note that conforming implementations are allowed to extend ECMAScript, so these are by no means 1:n relations; instead, this is the result of a comparison of most common language features.

See Language Features above for details.

List of Contributors

Thanks to (in alphabetical order):

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