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Using "this" in object literal

importance: 5

Here the function makeUser returns an object.

What is the result of accessing its ref? Why?

function makeUser() {
  return {
    name: "John",
    ref: this
  };
};

let user = makeUser();

alert( user.ref.name ); // What's the result?

Answer: an error.

Try it:

function makeUser() {
  return {
    name: "John",
    ref: this
  };
};

let user = makeUser();

alert( user.ref.name ); // Error: Cannot read property 'name' of undefined

That’s because rules that set this do not look at object definition. Only the moment of call matters.

Here the value of this inside makeUser() is undefined, because it is called as a function, not as a method with “dot” syntax.

The value of this is one for the whole function, code blocks and object literals do not affect it.

So ref: this actually takes current this of the function.

Here’s the opposite case:

function makeUser() {
  return {
    name: "John",
    ref() {
      return this;
    }
  };
};

let user = makeUser();

alert( user.ref().name ); // John

Now it works, because user.ref() is a method. And the value of this is set to the object before dot ..