How to access constructor function from object by using this

Question

In this example. I need to update friends list from object function.

var MyClass = function () {
    this.friends = [];
    this.runtime = {
        add: function (name) {
            this.friends.push(name);
        }
    }
};

MyClass.prototype.AddFriend = function (name) {
    this.runtime.add(name);
};

MyClass.prototype.GetFriends = function () {
    return this.friends;
};

How it's possible?

Urg. Why don't you just do `this.friends.push(name)` from that function? You're running into all kinds of crazy context issues there. — Andy, Apr 07 '15 at 13:24
@Andy I know that. But in my big project. I can't change total code. :( — Chandra Nakka, Apr 07 '15 at 13:33

score 1 · Answer 1 · answered Apr 07 '15 at 13:29

Like I said in the comments, it makes much more sense to use this.friends.push(name), but if you really have to use that odd runtime function, then you need to save a copy of this to a new variable:

var MyClass = function () {
    var _this = this;
    this.friends = [];
    this.runtime = {
        add: function (name) {
            _this.friends.push(name);
        }
    }
};

DEMO

score 1 · Accepted Answer · answered Apr 07 '15 at 13:42

1

You could also use the bind() method:

var MyClass = function () {
    this.friends = [];
    this.runtime = {
        add: function (name) {
            this.friends.push(name);
        }.bind(this)
    }
};

MyClass.prototype.AddFriend = function (name) {
    this.runtime.add(name);
};

MyClass.prototype.GetFriends = function () {
    return this.friends;
};

Read more about it here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind

answered Apr 07 '15 at 13:42

Peter Ringelmann

108
1
7

No problem. Although as @Andy rightly pointed out you should actually be using this.friends.push(name)...but if you really can't avoid scoping your functions like that then it will do the job. – Peter Ringelmann Apr 07 '15 at 13:56

How to access constructor function from object by using this

2 Answers2