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ECMAScript support in Web browsers

Netscape Navigator 3.0 shipped with JavaScript 1.1 in 1996. That same JavaScript 1.1 specification was

then submitted to the ECMA as a proposal for a new standard. With JavaScript’s explosive popularity,

Netscape was very happy to start developing version 1.2. One problem: ECMA hadn’t yet accepted

Netscape’s proposal.

A little after Netscape Navigator 3.0 was released, Microsoft introduced Internet Explorer 3.0. This ver-

sion of IE shipped with JScript 1.0 (Microsoft’s name for its JavaScript implementation), which was sup-

posed to be equivalent to JavaScript 1.1. However, because of undocumented and improperly replicated

features, JScript 1.0 fell far short of JavaScript 1.1.

Netscape Navigator 4.0 was shipped in 1997 with JavaScript 1.2 before the first edition of ECMA-262

was finalized; ECMA-262 was accepted and standardized later that year. As a result, JavaScript 1.2 is not

compliant to the first edition of ECMAScript, even though ECMAScript was supposed to be based on

JavaScript 1.1.

The next update to JScript occurred in Internet Explorer 4.0 with version JScript 3.0 (version 2.0 was

released in Microsoft’s Internet Information Server version 3.0 but was never included in a browser).

Microsoft put out a press release touting JScript 3.0 as the first truly ECMA-compliant scripting language

in the world. At that time, ECMA-262 hadn’t yet been finalized, so JScript 3.0 suffered the same fate as

JavaScript 1.2: It did not comply with the final ECMAScript standard.

Netscape opted to update its JavaScript implementation in Netscape Navigator 4.06. JavaScript 1.3

brought Netscape into full compliance with ECMAScript Edition 1. Netscape added support for the

Unicode standard and made all objects platform-independent while keeping the features that were intro-

duced in JavaScript 1.2.

When Netscape released its source code to the public as the Mozilla project, it was anticipated that

JavaScript 1.4 would be shipped with Netscape Navigator 5.0. However, a radical decision to completely

redesign the Netscape code from the bottom up threw a monkey wrench into the works. JavaScript 1.4

was only released as a server-side language for the Netscape Enterprise Server and never made it into a

Web browser.

Today, all popular Web browsers comply with the third edition of ECMA-262. The following table lists

ECMAScript support in the most popular Web browsers:

Browser

ECMAScript Compliance

Netscape Navigator 2.0

–

Netscape Navigator 3.0

–

Netscape Navigator 4.0–4.05

–

Netscape Navigator 4.06–4.79

Edition 1

Netscape 6.0+ (Mozilla 0.6.0+)

Edition 3

Internet Explorer 3.0

–

Internet Explorer 4.0

–

Table continued on following page

What Is JavaScript?

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