Initialization of object in javascript doesn't work at compile time

Question

I am trying to construct a javascript object as follows :

function returnA(){ return "A" }

function returnB(){ return "B" }

Now when I try,

obj = {returnA() : 1, returnB() : 2}

it gives me syntax error.

On the other way, when I do

obj = {};
obj[returnA()] = 1;
obj[returnB()] = 2;

It works perfectly. Why the first method of object initialization doesn't work, while the second one work ? Does there any difference in the time, when both are executed, I mean by that does first initialization takes place during compilation phase(static binding), while second initialization takes place on the fly, during runtime ?

Please help me out, as I am new to javascript.

Thanks in advance.

Edit : I needed to know the reason behind why it's happening. So, this question is different from the one marked as duplicate.

that is a syntax error, so getting a syntax error is not surprising ... p.s. javascript is not "compiled" as such — Jaromanda X, Dec 24 '15 at 12:00
It can in [ES2015](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#Computed_property_names) `obj = {[returnA()] : 1, [returnB()] : 2}` — adeneo, Dec 24 '15 at 12:02
I don't want how it can be done syntactically. I want to know grammatical reason behind it. — Mangu Singh Rajpurohit, Dec 24 '15 at 12:51

score 1 · Answer 1 · answered Dec 24 '15 at 12:01

obj = {returnA() : 1, returnB() : 2} , this obviously gives an error you can't assign to a result of a call.

obj = {};
obj[returnA()] = 1;
obj[returnB()] = 2;

this works because returnA() and returnB() will return a string which will become property names of the object

Initialization of object in javascript doesn't work at compile time

1 Answers1