Why won't .filter() work in Internet Explorer 8?

Array.filter() isn't included in IE until version 9.

You could use this to implement it:

if (!Array.prototype.filter){  Array.prototype.filter = function(fun /*, thisp */)  {    "use strict";    if (this === void 0 || this === null)      throw new TypeError();    var t = Object(this);    var len = t.length >>> 0;    if (typeof fun !== "function")      throw new TypeError();    var res = [];    var thisp = arguments[1];    for (var i = 0; i < len; i++)    {      if (i in t)      {        var val = t[i]; // in case fun mutates this        if (fun.call(thisp, val, i, t))          res.push(val);      }    }    return res;  };}

From: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/filter

Or since you are using jQuery, you can wrap your array into a jQuery object first:

songs = $(songs).filter(function(){  return this.album==album;}); 

Use es5-shim, so you can use filter/indexOf in IE8!

Facebook's react.js using that too.

  <!--[if lte IE 8]>  <script type="text/javascript" src="/react/js/html5shiv.min.js"></script>  <script type="text/javascript" src="/react/js/es5-shim.min.js"></script>  <script type="text/javascript" src="/react/js/es5-sham.min.js"></script>  <![endif]-->

https://github.com/es-shims/es5-shim

Does using the attr() function work?

songs = songs.filter(function (index) {    return $(this).attr("album") == album;});