var js = {
    filter: function(arr, callback) {
        var resp = [];
        for (i = 0; i < arr.length; i++) {
            if (callback.call(this, arr[i])) resp.push(arr[i]);
        }
        return resp;
    },

    map: function(arr, callback) {
        var resp = [];
        for (i = 0; i < arr.length; i++) {
            resp.push(callback.call(this, arr[i]));
        }
        return resp;
    }
}

var nums = [1, 2, 3, 4, 5];

var filter = js.map(nums, function(value) {
    return value > 2;
});

var mappy = js.map(nums, function(value) {
    return value * 2;
});

console.log(filter);
console.log(mappy);