Is the javascript .map() function supported in IE8?

The solution is jQuery.map

Instead of this: a.map(function( ) { });

You have to do

jQuery.map(a, function( ) { //what ever you want todo .. }

(function(fn){
    if (!fn.map) fn.map=function(f){var r=[];for(var i=0;i<this.length;i++)r.push(f(this[i]));return r}
    if (!fn.filter) fn.filter=function(f){var r=[];for(var i=0;i<this.length;i++)if(f(this[i]))r.push(this[i]);return r}
})(Array.prototype);

Put anywhere before first .map or .filter call. Problem solved. jQuery.map() method doesn't work as expected.

UPDATE: I've just tested it on sparse arrays: if map or filter argument is a function which accepts and handles undefined value - it works, but the results are not obvious:

Let's define test sparse array:

var t = []
t[1] = 1; t[3] = 3; t[5] = 5;

Let's see what does IE8 say about t: "[undefined, 1, undefined, 3, undefined, 5]"

Let's try:

t.filter(function(x){return x<4})

What is it, IE8? It's: "[1, 3]". Note - no undefined values. I would personally expect that.

But try THIS:

t.map(function(x){return 2<<x})

And... "[2, 4, 2, 16, 2, 64]". That's weird! :) Try this:

t.map(function(x){return Math.pow(2,x)})

And?... "[NaN, 2, NaN, 8, NaN, 32]" - I would rather expect this result for the previous test. It's at least logical - Math.pow() is supposed to return a number type, NaN, regardless of it's meaning IS a special number type reserved for invalid operations. So the result is more or less correct. It would be fully correct as map result if t remained a sparse array.

So without further ado - ultimately correct version of map and filter methods:

(function(fn){
    if (!fn.map) fn.map=function(f){var r=[];for(var i=0;i<this.length;i++)if(this[i]!==undefined)r[i]=f(this[i]);return r}
    if (!fn.filter) fn.filter=function(f){var r=[];for(var i=0;i<this.length;i++)if(this[i]!==undefined&&f(this[i]))r[i]=this[i];return r}
})(Array.prototype);

And the test:

var t = []; t[1] = 1; t[3] = 3; t[5] = 5;
var t1 = t.map(function(x){return 2<<x});
var t2 = t.filter(function(x){return x<10});
console.debug(t);
console.debug(t1);
console.debug(t2);

Expected results:

[object Array] [undefined, 1, undefined, 3, undefined, 5]

[object Array][undefined, 4, undefined, 16, undefined, 64]

[object Array][undefined, 1, undefined, 3, undefined, 5]

MDN says that IE 9 supports it. No mention of IE 8.

On MSDN it is said in Requirements for map: Not supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards.

Map is just a implementation of "Visitor" pattern for array. So easy substitute for it could be:

function visitArray(arr, visitor) {
    var result = [];

    for (var i = 0; i < arr.length; i ++) {
        result[i] = visitor(arr[i]);
    }

    return result;
}

The function also takes array and function which to invoke on each array element. It returns a new array with result of visitor invokation for each original array element