Is it possible to define a dynamically named property using object literal in JavaScript?

Question

Consider the following

var a = {foo: \"bar\"};

Equivalent to

var a = {};
a.foo = \"bar\";

Equivalent to

Answer 1

To answer your question, this is the only way that I know of. It uses eval. But beware, eval is evil!

var b = "foo";
var a = eval('({ ' + b + ': ' + '"bar"' + ' })');

This is an ugly solution. To play it safe you should not rely on this. Don't use it!

Answer 2

As others have said, no, there's currently no syntax for interpolated key strings in object literals in CoffeeScript; but it seems at some point this feature existed! In these GitHub issues there's some discussion about it: #786 and #1731.

It's implemented in Coco and LiveScript as:

b = 'foo'
a = {"#{b}": 'baz'}

# Or..
a = {(b): 'bar'}

Answer 3

JavaScript

var a, b;
(a = {})[b = 'foo'] = 'bar';

CoffeeScript

(a = {})[b = 'foo'] = 'bar'

Answer 4

No.

There is no way to do it using object literal notation.

---

UPDATE: According to the ECMAScript standard 6.0 you are now able to do the following:

var b = 'foo';
var a = { [b]: 'bar' };

console.log( a.foo );  // "bar"

However, this solution won't work in old browsers, which do not support ES6.

Answer 5

As of CoffeeScript version 1.9.1 this works:

b = "foo"
a = "#{b}": "bar"

It compiles to:

var a, b, obj;

b = "foo";

a = (
  obj = {},
  obj["" + b] = "bar",
  obj
);

Try it.

Answer 6

JSON parse allows you to convert a JSON string into an object:

JSON.parse('{"'+dynamicProperty+'":"bar"}');

This is not exactly an object litteral, but if your objective is to enter your property name as a variable it works.