How does Symbol work in ES6?

Symbol() is a new primitive. As Function , Object and Number .

What is special is that it generates something unique. A Symbol is always unique. Some people say that it generates tokens (because they are unique), always different.

That is:

var a = Symbol(123);
var b = Symbol(123);
console.log(a == b, a === b); // false, false

es6fiddle: link

This is true even interestingly in object property names.

var obj = {};
var a = obj[Symbol('prop')] = 'foo';
var b = obj[Symbol('prop')] = 'bar';
console.log(a, b, obj[Symbol('prop')]); // 'foo', 'bar', <vazio>

es6fiddle: link

Where can it be useful?

It's hard to guess all use cases, but some I imagine:

• Generate unique Symbols for ids and / or sessions
• avoiding object property name clashes

Good reading in English

• Axel Rauschmayer Blog: link
• MDN: link