Get even numbers from array using recursion instead of a loop, and without mutating the original array

array.js

Array.prototype.evens = function() {
    var arr = this;
    var out = [];
    var count = 0;
    var even = function(arr, out) {
        if (count <= arr.length - 1) {
            if ((arr[count] % 2) === 0) {
                out.push(arr[count]);
            }
            count++;
            even(arr, out);
        }
    };
    even(arr, out);
    return out;
}

var a = [1, 2, 3, 4, 5, 6, 7, 8, 9];

console.log(a);
console.log(a.evens());
console.log(a);​

Fiddle: http://jsfiddle.net/darren_n/uXt8S/