Object.assign()

Object.assign(target, ...sources)

Returns: object · Updated March 15, 2026 · Object Methods

object assign copy merge

Object.assign() copies all enumerable own properties from one or more source objects to a target object and returns the modified target. It’s commonly used for shallow cloning and merging objects.

Syntax

Object.assign(target, ...sources)

Parameters

Parameter	Type	Default	Description
`target`	`object`	—	The target object to receive properties
`sources`	`object`	—	One or more source objects to copy from

Examples

Basic object merging

const target = { a: 1 };
const source = { b: 2 };

const result = Object.assign(target, source);
console.log(result);
// { a: 1, b: 2 }

console.log(target);
// { a: 1, b: 2 } — target is mutated!

Merging multiple sources

const merged = Object.assign(
  { name: "JavaScript" },
  { version: "ES2024" },
  { feature: "top-level await" }
);

console.log(merged);
// { name: "JavaScript", version: "ES2024", feature: "top-level await" }

Shallow cloning an object

const original = { a: 1, b: 2 };
const clone = Object.assign({}, original);

console.log(clone);
// { a: 1, b: 2 }
console.log(clone === original);
// false

Common Patterns

Setting default options:

const defaults = { theme: "light", lang: "en" };
const userOptions = { theme: "dark" };

const options = Object.assign({}, defaults, userOptions);
console.log(options);
// { theme: "dark", lang: "en" }

Avoiding mutation — always use an empty {} as the target if you don’t want to mutate the original:

const obj = { x: 1 };
Object.assign(obj, { y: 2 }); // mutates obj — often unintended