`Array.prototype.filter` might not work on older browsers because it just got added in ECMAScript 5 (Yeah, < IE 9). You could create your own function that does something like this: http://underscorejs.org/#filter

Reference:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter (please don't modify the prototype as described in the article--I think it would be better if it was its own function for now).