ECMAScript: The Fifth Edition

1
ECMAScriptThe Fifth Edition

• Douglas Crockford
• Yahoo! Inc.
• http//crockford.com/codecamp/next.ppt

2
First new edition since 1999

• http//wiki.ecmascript.org/doku.php?ides3.1es3.1
  _proposal_working_draft
• The draft is being finalized.
• Please review it for correctness.
• It is closed to new features. You can still
  propose features for the Harmony edition.
• Testing will begin soon.
• It may be adopted by the ECMA General Assembly in
  December.

3
Interoperability

• ECMAScript is already one of the best languages
  when it comes to interoperability. It is getting
  even better.
• Much less is "implementation dependent".
• Common practice is now reflected in the standard.
• Three-out-of-four.

4
Security

• Strict Mode.
• Object hardening.
• Properties can be protected from modification.
• We still have a global object, so it is still an
  insecure language.
• A step backwards We now have getters and setters.

5
"use strict"

• Optional strict mode.
• Don't use it unless you mean it.
• Removes some of the most problematic features
  from the language.
• Limitations on eval, arguments, delete, with
• This will help improve confidence in Caja,
  ADsafe, and other safety measures.
• Possible performance benefit.

6
Syntax Relaxation

• object.for and object.class are now legal.
• extra "comma", is now legal.
• 1,2,3,.length 3
• ltBOMgt is now whitespace.

7
Strings

• \ltLFgt now allowed in string literals.
• string.trim()

8
Arrays

• Array.isArray(array)
• array.indexOf(searchElement, fromIndex)
• array.lastIndexOf(searchElement, fromIndex)
• array.every(func, thisArg)
• array.some(func, thisArg)
• array.forEach(func, thisArg)
• array.map(func, thisArg)
• array.filter(func, thisArg)
• array.reduce(func, initialValue)
• array.reduceRight(func, initialValue)

9
Objects

• Object.create(object, properties)
• Object.keys(object)
• Object.getOwnPropertyNames(object)
• Object.getPrototypeOf(object)
• Object.defineProperty(object, name, attributes)
• Object.defineProperties(object, properties)
• Object.getOwnPropertyDescriptor(object, name)
• Object.preventExtensions(object)
• Object.seal(object)
• Object.freeze(object)
• Object.isExtensible(object)
• Object.isSealed(object)
• Object.isFrozen(object)

value enumerable
writeable configurable get
set
10
Dates

• Support for ISO dates.
• Date.now()
• date.toISOString ( )

11
Functions

• function.bind(this, args...)
• function.apply no longer wraps or replaces its
  this parameter.

12
arguments

• arguments still isn't an array, but it is more
  array-like.
• arguments now inherits from Array.prototype, so
  these two statements do the same thing
• arguments.slice(2)
• Array.prototype.slice.apply(arguments, 2)
• arguments is still dangerously linked to
  parameters.

13
Regular Expressions

• RegExp literals now produce unique objects.
• \s now describes all of the whitespace characters
  recognized by the language.
• /// is now legal.

14
JSON

• JSON.parse(text, reviver)
• JSON.stringify(value, replacer, indent)
• http//www.json.org/json2.js
• http//wiki.ecmascript.org/doku.php?ides3.1es3.1
  _proposal_working_draft