Question

As detailed elsewhere, and otherwise apparently well-known, Internet Explorer (definitely version 7, and in some instances, version 8) do not implement key functions, in particular on Array (such as forEach, indexOf, etc).

There are a number of workarounds here and there, but I’d like to fold a proper, canonical set of implementations into our site rather than copy and paste or hack away at our own implementations. I’ve found js-methods, which looks promising, but thought I’d post here to see whether another library comes more highly-recommended. A couple of miscellaneous criteria:

• The library should just be a no-operation for those functions that a browser already has implementations for (js-methods appears to do quite well here).
• Non-GPL, please, though LGPL is acceptable.

Answer 1

Many use the MDC fallback implementations (eg. for indexOf). They’re generally rigorously standards-compliant, even to the extent of explicitly checking the types of all the arguments.

Unfortunately whilst it is clear that the authors regard this code as trivial and freely-usable, there doesn’t seem to be an explicit licence-grant to put this in writing. The wiki as a whole is CC Attribution-ShareAlike, if that’s an acceptable licence (though CC isn’t designed for code as such).

js-methods looks OK in general, but is not as standards-compliant around the edges of how the functions are supposed to be (eg. undefined list items, functions that mutate the list). It’s also full of other random non-standard methods, including some questionable ones like the dodgy stripTags and the incomplete UTF-8 codec (which is also a bit unnecessary given the unescape(encodeURIComponent) trick).

For what it’s worth, here’s what I use (which I hereby release into the public domain, if it can be said to be copyrightable at all). It’s a bit shorter than the MDC versions as it doesn’t attempt to type-sniff that you haven’t done something silly like pass non-function callbacks or non-integer indexes, but apart from that it attempts to be standards-compliant. (Let me know if I’ve missed anything. ;-))

'use strict';

// Add ECMA262-5 method binding if not supported natively
//
if (!('bind' in Function.prototype)) {
    Function.prototype.bind= function(owner) {
        var that= this;
        if (arguments.length<=1) {
            return function() {
                return that.apply(owner, arguments);
            };
        } else {
            var args= Array.prototype.slice.call(arguments, 1);
            return function() {
                return that.apply(owner, arguments.length===0? args : args.concat(Array.prototype.slice.call(arguments)));
            };
        }
    };
}

// Add ECMA262-5 string trim if not supported natively
//
if (!('trim' in String.prototype)) {
    String.prototype.trim= function() {
        return this.replace(/^\s+/, '').replace(/\s+$/, '');
    };
}

// Add ECMA262-5 Array methods if not supported natively
//
if (!('indexOf' in Array.prototype)) {
    Array.prototype.indexOf= function(find, i /*opt*/) {
        if (i===undefined) i= 0;
        if (i<0) i+= this.length;
        if (i<0) i= 0;
        for (var n= this.length; i<n; i++)
            if (i in this && this[i]===find)
                return i;
        return -1;
    };
}
if (!('lastIndexOf' in Array.prototype)) {
    Array.prototype.lastIndexOf= function(find, i /*opt*/) {
        if (i===undefined) i= this.length-1;
        if (i<0) i+= this.length;
        if (i>this.length-1) i= this.length-1;
        for (i++; i-->0;) /* i++ because from-argument is sadly inclusive */
            if (i in this && this[i]===find)
                return i;
        return -1;
    };
}
if (!('forEach' in Array.prototype)) {
    Array.prototype.forEach= function(action, that /*opt*/) {
        for (var i= 0, n= this.length; i<n; i++)
            if (i in this)
                action.call(that, this[i], i, this);
    };
}
if (!('map' in Array.prototype)) {
    Array.prototype.map= function(mapper, that /*opt*/) {
        var other= new Array(this.length);
        for (var i= 0, n= this.length; i<n; i++)
            if (i in this)
                other[i]= mapper.call(that, this[i], i, this);
        return other;
    };
}
if (!('filter' in Array.prototype)) {
    Array.prototype.filter= function(filter, that /*opt*/) {
        var other= [], v;
        for (var i=0, n= this.length; i<n; i++)
            if (i in this && filter.call(that, v= this[i], i, this))
                other.push(v);
        return other;
    };
}
if (!('every' in Array.prototype)) {
    Array.prototype.every= function(tester, that /*opt*/) {
        for (var i= 0, n= this.length; i<n; i++)
            if (i in this && !tester.call(that, this[i], i, this))
                return false;
        return true;
    };
}
if (!('some' in Array.prototype)) {
    Array.prototype.some= function(tester, that /*opt*/) {
        for (var i= 0, n= this.length; i<n; i++)
            if (i in this && tester.call(that, this[i], i, this))
                return true;
        return false;
    };
}

Other ECMA262-5 methods not implemented here include Array reduce/reduceRight, the JSON ones and the few new Object methods that can be reliably implemented as JS functions.