Generic function?

Question

I'm trying to figure out the answer to this question:

Without using Javascript's bind function, implement the magic function so that:

var add = function(a, b) { return a + b; }
var addTo = add.magic(2);

var say = function(something) { return something; }
var welcome = say.magic('Hi, how are you?');

addTo(5) == 7;
welcome() == 'Hi, how are you?';

I think I need to use call or apply but I just don't know, if someone could point me in the right direction or provide some literature it would be much appreciated.

Answer 1

You can use closure, and apply function

Function.prototype.magic = function(){
  var self = this;
  var args = Array.from(arguments);
  
  return function(){
    return self.apply(null, args.concat(Array.from(arguments)));
  }
}


var add = function(a, b) { return a + b; }
var addTo = add.magic(2);

var say = function(something) { return something; }
var welcome = say.magic('Hi, how are you?');

console.log(addTo(5) == 7);
console.log(welcome() == 'Hi, how are you?');

---

Also you can look to Polyfill for bind function on MDN

Answer 2

Please see below code:

    Object.prototype.magic = function (message) {
        alert(message);
    }
    var add = function (a, b) { return a + b; }
    var addTo = add.magic(2);

    var say = function (something) { return something; }
    var welcome = say.magic('Hi, how are you?');

    addTo(5) == 7;
    welcome() == 'Hi, how are you?';