Internet Explorer 9 Guide for Developers

ECMAScript 5

Internet Explorer 9 introduces enhancements to the JavaScript language feature in addition to improved JavaScript performance. In December 2009, ECMA approved the Fifth Edition of ECMA-262 as the successor to the Third Edition (a Fourth Edition was never published), and that same year, Microsoft debuted elements of ECMAScript 5 (ES5) support when native JSON support for JavaScript objects was added to Internet Explorer 8 and Accessor Support for DOM objects was added to Internet Explorer 8. Beyond JSON and DOM Accessor support, though, ES5 standardizes many significant enhancements to the JavaScript language.

There are many important ECMAScript 5 features implemented in Internet Explorer 9, including the following:

• New array methods: every, filter, forEach, indexOf, isArray, lastIndexOf, map, reduce, reduceRight, some
• Enhanced object model and object functions: Object.create, Object.defineProperties, Object.defineProperty, Object.freeze, Object.getOwnPropertyDescriptor, Object.getOwnPropertyNames, Object.getPrototypeOf, Object.isExtensible, Object.isFrozen, Object.isSealed, Object.keys, Object.preventExtensions, Object.seal
• Other computational methods and functions: Date.now, Date.parse support for ISO Date Format, Date.toISOString, Function bind, String trim

Internet Explorer 9 also corrects several issues present in the previous implementations of JavaScript in Internet Explorer. For more information, see the Internet Explorer Team Blog. To see ECMAScript 5 support in action, go to the Internet Explorer Test Drive site.