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JavaScript Symbols

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.

Syntax

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

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