remove duplicates in javascript

gistfile1.txt

function removeDups(array) {
    var obj = {},
        len = array.length,
        res = [],
        i;

    for(i=0; i < len; i++) {
        obj[JSON.stringify(array[i])] = array[i];
    }

    for(i in obj) {
        res.push(obj[i]);
    }

    return res;
}

配列のunique化ですね。
ES5.1において、JSON.stringifyはNaN、Infinity、-Infinityを'null'にします。

NOTE 4 Finite numbers are stringified as if by calling ToString(number). NaN and Infinity regardless of sign are represented as the String null.

ECMAScript Language Specification - ECMA-262 Edition 5.1

null、NaN、Infinity、-Infinity、+0、-0、Object、RegExp、Functionを厳密に区別すると以下の様な実装になりますね。

/*jslint maxlen: 80*/
// Edition 2012-07-10

function arrayUnique(arr) {
    'use strict';

    var results, objList, primHash, i, arrLen, val, type, objListLen,
        contain, key;

    results = [];
    objList = [];
    primHash = {};

    for (i = 0, arrLen = arr.length; i < arrLen; i += 1) {
        val = arr[i];
        type = typeof val;

        if (val && (type === 'object' || type === 'function')) {
            objListLen = objList.length;
            contain = false;

            while (objListLen) {
                contain = val === objList[objListLen -= 1];

                if (contain) {
                    break;
                }
            }

            if (!contain) {
                objList.push(val);
                results.push(val);
            }
        } else {
            key = (val === 0 && 1 / val === -Infinity)
                ? type + '-' + val
                : type + val;

            if (!primHash[key]) {
                primHash[key] = true;
                results.push(val);
            }
        }
    }

    return results;
}