How to Create Symbol in JavaScript: Syntax and Examples

In JavaScript, you create a symbol using the Symbol() function, which returns a unique and immutable value. You can optionally pass a description string to Symbol() to help identify the symbol during debugging.

Syntax

The basic syntax to create a symbol is using the Symbol() function. You can optionally provide a description as a string to help identify the symbol.

• Symbol(): Creates a new unique symbol.
• Symbol(description): Creates a symbol with a description for debugging.

javascript

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

Example

This example shows how to create symbols and use them as unique keys in an object. Symbols ensure the keys do not clash with other properties.

javascript

const id = Symbol('id');
const user = {
  name: 'Alice',
  [id]: 12345
};

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

// Symbols are unique even with the same description
const symA = Symbol('id');
console.log(id === symA); // false

Output

Alice
12345
false

Common Pitfalls

Common mistakes when using symbols include:

• Trying to access symbol properties with dot notation instead of bracket notation.
• Assuming symbols with the same description are equal (they are always unique).
• Using symbols as keys but forgetting they are not enumerable by default.

javascript

const sym = Symbol('key');
const obj = {};

// Wrong: obj.sym = 'value'; // This creates a string key 'sym', not a symbol key

// Right:
obj[sym] = 'value';

console.log(obj[sym]); // 'value'

Output

'value'

Quick Reference

Concept	Description
Symbol()	Creates a new unique symbol
Symbol(description)	Creates a symbol with a description string
Symbol keys	Use bracket notation to access symbol properties
Uniqueness	Symbols are always unique, even with same description
Non-enumerable	Symbol properties do not show up in for...in loops

Key Takeaways

Use Symbol() to create unique and immutable identifiers in JavaScript.

Always use bracket notation to access or assign symbol-keyed properties.

Symbols with the same description are different and unique values.

Symbol properties are not enumerable by default and won't appear in normal loops.

Descriptions help debugging but do not affect symbol uniqueness.