JavaScript: Comparing arrays, objects for sameness [closed]

I would separate array and object comparison.

And for arrays, another way to proceed can also be to use the algorithm given here: http://www.shamasis.net/2009/09/fast-algorithm-to-find-unique-items-in-javascript-array/

function getArrayWithoutDuplicates (anArray) { //derived from shamasis.net
    var o = {}, i, l = anArray.length, r = [];
    for(i=0; i<l;i+=1) o[anArray[i]] = anArray[i];
    for(i in o) r.push(o[i]);
    return r;
};

function arrayCompare(array1, array2, ignoreOrder){
    if(array1.length != array2.length) {return false;}

    var wdArray1 = getArrayWithoutDuplicates(array1);
    var wdArray2 = getArrayWithoutDuplicates(array2);
    if(ignoreOrder){
        wdArray1 = sort(wdArray1);
        wdArray2 = sort(wdArray2);
    }
    for(var i = 0; i < wdArray1.length; i++){
        if(wdArray1[i] != wdArray2[i]){return false;}
    }
    //If not returned until there, then arrays are identical
    return true;
}

This could be used depending on your needs in terms of performance, and the performance of JSON.stringify compared to this algorithm.

All technical questions aside, I don't really see a big need for such a function. Any sane programmer would try to avoid using such an expensive function, and I just can't think of any legitimate situation where you want a complete compare.

First off, about the "name" of the function: I'm not sure if extending the Object object is a good idea. It wasn't until recently (ECMAScript5 agian), that Object didn't have any such "class methods", and I don't know if other scripts may trip over them.

I don't know if it's by design, but if not, your code has a serious bug: When comparing two objects with ignoreOrder == true, then your function will return true, when the objects have different member names, but the same member values, for example:

Object.identical({a:1, b:2}, {x: 1, y:2}, true); //returns true

Personally I find distinguishing between "sorted" and "unsorted" objects or "sorting" objects at all a bit strange, because by definition the members of an object don't have an order. For all intents and purposes {a: 1, b: 2} and {b: 2, a: 1} are identical and should be always handled that way. This also leads to wondering if stringify() is the right tool to compare objects, because that wouldn't considered those two examples the same.

I think functions as defined in this StackOverflow question as much more reliable and in the spirit of how JavaScript objects are defined.

Here is a table of all the browsers that support ECMAScript5. It looks like only the newest browsers (FF4, IE9) support it, so if you're only running on those or are willing to limit your site to those, you're fine. Otherwise, refactor to earlier code.

This SO answer gives a JavaScript solution to equality that I believe will work more widely.