For example, Tamarin – the virtual machine for ActionScript, developed and open-sourced by Adobe – has just-in-time compilation (JIT) support for certain classes of scripts.
In late 2007, a debate between Eich, later the Mozilla Foundation's CTO, and Chris Wilson, Microsoft's platform architect for Internet Explorer, became public on a number of blogs.
[22] Eich responded by stating that Wilson seemed to be "repeating falsehoods in blogs" and denied that there was attempt to suppress dissent and challenged critics to give specific examples of incompatibility.
[23] He pointed out that Microsoft Silverlight and Adobe AIR rely on C# and ActionScript 3 respectively, both of which are larger and more complex than ECMAScript Edition 3.
[25][26] In April 2009, Ecma TC39 published the "final" draft of the 5th edition and announced that testing of interoperable implementations was expected to be completed by mid-July.
Other new features include iterators and for...of loops, Python-style generators, arrow function expression (() => {...}), let keyword for local declarations, const keyword for constant local declarations, binary data, typed arrays, new collections (maps, sets and WeakMap), promises, number and math enhancements, reflection, proxies (metaprogramming for virtual objects and wrappers) and template literals using backticks (`) for multi-line strings without escape characters.
[5] Its features include exponentiation operator ** for numbers, await, async keywords for asynchronous programming (as a preparation for ES2017), and the Array.prototype.includes function.
[5] The exponentiation operator is equivalent to Math.pow, but provides a simpler syntax similar to languages like Python, F#, Perl, and Ruby.
[7] New features include the spread operator and rest parameters (...) for object literals, asynchronous iteration, Promise.prototype.finally and additions to RegExp.
[9] In addition to new functions, this version introduces a BigInt primitive type for arbitrary-sized integers, the nullish coalescing operator, and the globalThis object.
BigInts allow the representation and manipulation of integers beyond Number.MAX_SAFE_INTEGER, while Numbers are represented by a double-precision 64-bit IEEE 754 value.
This contrasts with the || operator, which would return "string" for all "falsy" values, such as the ones below.Optional chaining makes it possible to access the nested properties of an object without having an AND check at each level.
?=, &&=, ||=); WeakRef, for referring to a target object without preserving it from garbage collection, and FinalizationRegistry, to manage registration and unregistration of cleanup operations performed when target objects are garbage collected; separators for numeric literals (1_000); and Array.prototype.sort was made more precise, reducing the number of cases that result in an implementation-defined sort order.
[11] This version introduces top-level await, allowing the keyword to be used at the top level of modules; new class elements: public and private instance fields, public and private static fields, private instance methods and accessors, and private static methods and accessors; static blocks inside classes, to perform per-class evaluation initialization; the #x in obj syntax, to test for presence of private fields on objects; regular expression match indices via the /d flag, which provides start and end indices for matched substrings; the cause property on Error objects, which can be used to record a causation chain in errors; the at method for Strings, Arrays, and TypedArrays, which allows relative indexing; and Object.hasOwn, a convenient alternative to Object.prototype.hasOwnProperty.
[38] This version introduces the Object.groupBy and Map.groupBy static methods, Promise.withResolvers, various set operations on Set.prototype, and the /v unicode flag for regular expressions.
The language committee follows a "living spec" model, so these changes are part of the standard, and ratification is a formality.