JavaScript Symbols

• JavaScript Symbol Prototype Methods

Description

These are tokens that serve as unique IDs. You create symbols via the factory function Symbol() (which is loosely similar to string returning strings if called as a function).

Syntax

const symbol1 = Symbol();

Add a description

const tralala = Symbol('tralala')
console.log(tralala) // Symbol(tralala)

Convert to string

const tralala = Symbol('tralala')
console.log(String(tralala)) // `Symbol(tralala)`

Every Symbol is unique

console.log(Symbol() === Symbol()) // false

Property keys

const KEY = Symbol();
const obj = {};
 
obj[KEY] = 123;
console.log(obj[KEY]); // 123

const FOO = Symbol();
const obj = {
    [FOO]() {
        return 'bar';
    }
};
console.log(obj[FOO]()); // bar

Use as reserved inherited method names

If for some bizarre reason you want to use reserved inherited method names yourself (like toString) you can with Symbols.

const toStringSymbol = Symbol("toString");
Array.prototype[toStringSymbol] = function() {
  return `${this.length} cm of blue yarn`;
};
 
console.log([1, 2].toString()); //1, 2
console.log([1, 2][toStringSymbol]()); // 2 cm of blue yarn

Expressions

Symbols can also be used in object expressions and classes.

const toStringSymbol = Symbol("toString");
 
let stringObject = {
  [toStringSymbol]() {
    return "a jute rope";
  },
};
console.log(stringObject[toStringSymbol]()); // a jute rope