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Creating Symbols

Creating Symbols

Introduction

Symbols are created using the Symbol() function. Each call creates a completely unique value.

Symbol() — Unique Symbols

const sym1 = Symbol('debug');
const sym2 = Symbol('debug');

console.log(sym1 === sym2); // false — every Symbol is unique!
console.log(typeof sym1);   // 'symbol'
console.log(sym1.toString()); // 'Symbol(debug)'

Symbol.for() — Global Registry

const sym1 = Symbol.for('app.id');
const sym2 = Symbol.for('app.id');

console.log(sym1 === sym2); // true — same symbol from registry
console.log(Symbol.keyFor(sym1)); // 'app.id'

Symbol() vs Symbol.for()

Aspect	`Symbol()`	`Symbol.for()`
Uniqueness	Always unique	Shared globally
Same description	Different symbols	Same symbol
Use case	Private, unique keys	Cross-realm sharing

Using Symbols as Property Keys

const id = Symbol('id');

const user = {
  name: 'Alice',
  [id]: 12345  // Symbol as property key
};

console.log(user[id]);   // 12345
console.log(user.name);  // 'Alice'

// Symbols don't appear in normal enumeration
console.log(Object.keys(user));           // ['name']
console.log(JSON.stringify(user));        // {'name':'Alice'}
console.log(Object.getOwnPropertySymbols(user)); // [Symbol(id)]

Summary

Symbol() creates unique, private keys
Symbol.for() creates/retrieves global symbols
Symbols as property keys are hidden from normal iteration
Object.getOwnPropertySymbols() retrieves symbol keys
Great for metadata, private properties, and framework internals

Further Reading