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ECMAScript 3.1 Final Draft Emerges

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Also known as ECMAScript 5th Edition, the new JavaScript standard has entered final draft stage. Among the goodies: a formal getter and setter syntax for object properties, language reflection features, support for the JSON data format, additional Array methods, and a strict mode that improves error checking.

Function.bind

Function.prototype.bind(self, args...). A bind function wraps a function in a closure, storing references to the context arguments from the surrounding scope. This is somewhat equivalent to the following:

Function.prototype.bind = function(context) {
  var fun = this;
  return function(){
    return fun.apply(context, arguments);
  };
};

Applications include partial application of arguments to a function and currying. Though you can custom-roll one today, a native bind function in 3.1 should outperform any equivalent user-defined function.

Array

The additional Array methods in ECMAScript 3.1 are identical to methods introduced in JavaScript 1.6-1.8, but were never present in any official ECMAScript specification. They are currently implemented in Firefox 3.x. Of course, having them in ECMAScript 3.1 means that now you will be able to actually use them (provided, of course, that all browsers implement the standard...). These methods are: indexOf, lastIndexOf, filter, forEach, every, map, some, reduce, and reduceRight. There's a good description of each method here.

ECMAScript 3.1, also known as JavaScript Harmony, is the less ambitious version of what was to be JavaScript 2/ECMAScript 4, a plan scuttled when some members of ECMA balked at the large additions to the language.

The new specification is available here.