Javascript Array rawr(f)

// complete the implementation of triple and map such that
// [0,3,6,9,12] is printed

var arr = [0,1,2,3,4];

var triple = function(x) { return x * 3; };

Array.prototype.rawr = function(f) {
    var newArr =[];
    /*from   w  w  w .ja  v a2  s .  c  o  m*/
    for (var i = 0; i < this.length; i++) {
        newArr.push(f(this[i]));
    }
    return newArr;
};

var newArr = arr.rawr(triple);
console.log(newArr);

console.log("using map this time");
console.log(arr.map(triple));