Javascript Array numberOfOccurrences(arr)

//The numberOfOccurrences function must return the number of occurrences of an element in an array.var arr = [0,1,2,2,3];
//arr.numberOfOccurrences(0) === 1;
//arr.numberOfOccurrences(4) === 0;
//arr.numberOfOccurrences(2) === 2;
//arr.numberOfOccurrences("a") === 0;

Array.prototype.numberOfOccurrences = function (arr) {
    var elem = 0;
    for (var i = 0; i < this.length; i++) {
        if (this[i] === arr) {
            elem++;/*from ww w .  j  a  v a  2s.co  m*/
        }
    }
    return elem;
};