“We expect the Fifth Edition to benefit all Web developers by helping improve browser interoperability and making enhanced scripting features broadly available,” added Allen Wirfs-Brock, an ECMAScript architect at Microsoft.

Mozilla and Microsoft were initially at odds on which evolutionary path ECMAScript should take. Mozilla and supporting companies such as Adobe were pushing a more ambitious goal for ECMAScript in a specification called ECMAScript 4.0. However, Microsoft and supporters such as Yahoo were in support of the ECMAScript 3.1 standard, or what is now known as ECMAScript, Fifth Edition.

Indeed, the last major revision of the ECMAScript standard was the Third Edition, published in 1999. After completion of the Third Edition, much effort was put into developing a Fourth Edition. Although the so-called Fourth Edition was not completed, that work influenced ECMAScript, Fifth Edition, and is continuing to influence the ongoing development of ECMAScript, Ecma said. Work on future ECMAScript editions continues as part of the previously announced ECMAScript Harmony project.

According to Ecma, the Fifth Edition of ECMAScript codifies de facto interpretations of the language specification that have become common among browser implementations and adds support for new features that have emerged since the publication of the Third Edition. Such features include accessor properties, reflective creation and inspection of objects, program control of property attributes, additional array manipulation functions, support for the JSON object encoding format, and a strict mode that provides enhanced error checking and program security.

Ecma went a little deeper regarding the ECMAScript candidate specification:

“The ECMAScript, Fifth Edition candidate specification has been developed by Ecma TC39 whose membership includes all major browser vendors. The Candidate milestone designates that the authoring process is complete. This now begins a testing and validation phase of the project where TC39 members will create and test implementations of the candidate specification to verify its correctness and the feasibility of creating interoperable implementations. The test implementations will also be used for web compatibility testing to ensure that the revised specification remains compatible with existing web applications. TC39 members Opera, Mozilla, and Microsoft have each committed to participating in this testing process. Testing is expected to be complete by mid-July 2009. It is anticipated that any technical errors and ambiguities will be resolved during this process, and that a final draft of the specification can be agreed upon in September for submission to the Ecma General Assembly for final approval in December 2009. It is anticipated that this will result in a fast-track submission to ISO/IEC JTC 1 for revision of ISO/IEC 16262.”

Meanwhile, in a blog post, the Microsoft representatives on the TC39 committee, Wirfs-Brock and Pratap Lakshman, said:

“The goal of this revision was to update the ECMAScript specification to reflect the language as it is actually implemented in modern web browsers and to establish a foundation for the future evolutions of the language. … Many of these features standardize enhanced functionality that has been provided by individual browsers but has not yet been universally adopted.”

The Microsoft duo also said:

“For the average web developer the release of a candidate specification has little immediate impact because you have to create content that works with the browser versions that are actually in use today.  However, we expect that once it is finally approved, the revised ECMAScript standard to be widely and fairly rapidly adopted by browsers.  In the meantime, this new specification is already having an impact.  For example, in IE8 both the native JSON and the DOM Prototypes features are based upon APIs defined in the ECMAScript Fifth Edition Specification.”