ES6 Symbols in Chrome

Question

I'm experimenting with the new ES6 Symbols in Google Chrome, and after enabling "Experimental JavaScript" in Chrome Flags, I can use new Symbol() in my code.

However, when I try to run the following code:

var sym = new Symbol();
var obj = {};
obj[sym] = 'Hello, symbols';

I get the following error:

TypeError: Conversion from symbol to string

What's wrong with my code?

Thanks!

Answer 1

Since symbols are values, not objects, they are created by a plain function call to Symbol, not by invoking new on it. In the version of Chrome you are using, new Symbol gives you a wrapper object for such a value (i.e., you can get the actual symbol by invoking .valueOf on the result).

Since this is a common pitfall, the ES6 draft spec recently changed to disallow constructor invocation of Symbol altogether. That is, you already get an exception on the first line of your code. This change has already been implemented in V8, but hasn't made it into Chrome yet.