bind_js2.js

var first_object = {
    num: 4
};

function multi(mul) {
    return this.num * mul;
}

Function.prototype.bind = function (obj) {
    var method = this,
        temp = function () {
            return method.apply(obj, arguments);
        };

    return temp;
}

var first_mul = multi.bind(first_object);
console.log(first_mul(5)); //20