← Back to Roadmap

Symbol

Medium

In plain terms

Symbol creates unique identifiers. Every Symbol() is unique. Used for object property keys to avoid collisions. Symbol.iterator defines iteration. Primitives, not objects.

What you need to know

  • •Unique every time
  • •Used for hidden/private keys
  • •Symbol.iterator, etc.

Try it yourself

Copy the code below and run it in your browser console or a code editor:

const id1 = Symbol();
const id2 = Symbol();
id1 === id2;  // false

const ID = Symbol('id');
const user = {
  [ID]: 123,
  name: 'Alice'
};
user[ID];  // 123

// Well-known symbols
const obj = {
  [Symbol.iterator]: function*() {
    yield 1;
    yield 2;
  }
};

Learn more

Dive deeper with these trusted resources:

MDNjavascript.infoTutorialsPointW3Schools