What happened when javascript engine interpret object literal?

Question

Recently I tried to create an object using object literal. And I need a property that use another property in the object. Like this

var object = {
    property1:'property1',
    property2:'property2 is from ' + this.property1
};
console.log(object.property2);// property2 is from undefined

The this.property1 is undefined in the property2.

I do know many ways to deal with this problem. My question is what happens behind the scenes? In other words, how javascript engine interpret object literal? I know "hoisting" happens in the function. Does "hoisting" happens in object literal?

Thanks.

`this` is function scoped, not object-initializer scoped. – Oriol Nov 04 '15 at 23:21 — Oriol, Nov 04 '15 at 23:21

score 2 · Accepted Answer · answered Nov 04 '15 at 23:18

That's what happens:

this refers to the scope where your code is running.

The same way in this code:

var a = 42;

var o = {
    key: a
};

a is resolved from the current scope, the this reference in your code is resolved to whatever this refers to "outside" of an object literal. (quotes with "outside" are used since there is no any "inside" or "outside" of literal - all the code runs in the current scope).

So technically your code could be transformed to something like

var a = this;

var object = {
    property1:'property1',
    property2:'property2 is from ' + a.property1
};

or even

var p = this.property1;

var object = {
    property1:'property1',
    property2:'property2 is from ' + p
};

so that some special properties of this did not confuse you.

What happened when javascript engine interpret object literal?

1 Answers1