In the code below, when somethingUseful.thisUsefulThing is called from setTimeout, can it reference somethingUseful.thatUsefulThing?

var somethingUseful = {
  thisUsefulThing: function() {
    this.thatUsefulThing();
  },

  thatUsefulThing: function() {
    console.log("I am useful!");
  }
}

setTimeout(somethingUseful.thisUsefulThing, 1000);

Right now, I am getting this error:

Uncaught TypeError: Object [object global] has no method 'thatUsefulThing'

In the code below, when somethingUseful.thisUsefulThing is called from setTimeout, can it reference somethingUseful.thatUsefulThing?

var somethingUseful = {
  thisUsefulThing: function() {
    this.thatUsefulThing();
  },

  thatUsefulThing: function() {
    console.log("I am useful!");
  }
}

setTimeout(somethingUseful.thisUsefulThing, 1000);

Right now, I am getting this error:

Uncaught TypeError: Object [object global] has no method 'thatUsefulThing'

• javascript
• function
• dictionary
• this

• 6 What do you mean "scope of global" vs "scope of the object"? Your code as written works. – user2736012 Commented Oct 23, 2013 at 23:22
• 1 Just keep in mind that when you do object.method(), the value of this in method bees a reference to object. Makes no difference where or when the object and method were created. All that matters is how you call the method. Put that same method on a different object, call it from that object, and the value of this will refer to the new object. var o = {thatUsefulThing:function() {console.log("I'm useful too!");}}; o.foo = somethingUseful.thisUsefulThing; o.foo(); // I'm useful too – user2736012 Commented Oct 23, 2013 at 23:32
• There, I edited it to directly reflect the error I'm encountering in a nutshell. – Synthead Commented Oct 23, 2013 at 23:38
• That's because you're sending the method to setTimeout by detaching it from the object. Remember, this is determined by how the method is called. When you do object.method(), the method can see that it is being called from object so this bees object. If you detach it, as I showed in my ment above, its this will be based on how it was now being called. If it's not called from some object, it gets the default window object. – user2736012 Commented Oct 23, 2013 at 23:42
• ...to keep them joined, pass an anonymous function that invokes the method from the object. setTimeout(function() {somethingUseful.thisUsefulThing();}, 1000); – user2736012 Commented Oct 23, 2013 at 23:44

2 Answers 2

To simply answer your question, YES, thisUsefulThing CAN access thatUsefulThing

But as your code currently runs, 'this' is not actually global, it is a reference to somethingUseful to all direct descendants itself.

When I am working with literal objects, I usually reference them by name rather than with 'this', so in your case I would replace 'this.thatUsefulThing()' with somethingUseful.thatUsefulThing()

Why? Because it works globally, anyway!

EDIT:

As plalx pointed out in his ment to my answer, best practices for implementing this class (with an example class member) would use functional classes / prototypes and look something like this:

function SomethingUseful () {
    this.member = 'I am a member';
}
SomethingUseful.prototype.thisUsefulThing = function () {
    this.thatUsefulThing();
}
SomethingUseful.prototype.thatUsefulThing = function () {
    console.log('I am useful, and ' + this.member);
}
usefulObject = new SomethingUseful();

usefulObject.thisUsefulThing(); // logs fine with access to this.member
setInterval(usefulObject.thisUsefulThing.bind(usefulObject), 1000); // has access to this.member through bind()

Just bind the this value to somethingUseful.

setTimeout(somethingUseful.thisUsefulThing.bind(somethingUseful), 1000);