docs/reference/compat/object/assign.md
::: warning Use Object.assign instead
This assign function operates slowly due to additional logic that checks whether values are equal.
Use the faster and more modern Object.assign instead.
:::
Assigns properties from source objects to a target object.
const result = assign(target, ...sources);
assign(target, ...sources)Use assign when you want to copy properties from one or more source objects to a target object. If there are duplicate keys, values from later sources will overwrite earlier ones.
import { assign } from 'es-toolkit/compat';
// Basic usage
const target = { a: 1, b: 2 };
const source = { b: 3, c: 4 };
const result = assign(target, source);
// Result: { a: 1, b: 3, c: 4 }
console.log(target === result); // true (target object is modified)
// Merging multiple source objects
const target2 = { a: 1 };
const source1 = { b: 2 };
const source2 = { c: 3 };
const source3 = { d: 4 };
assign(target2, source1, source2, source3);
// Result: { a: 1, b: 2, c: 3, d: 4 }
// Overwriting properties
const target3 = { x: 1, y: 2 };
const source4 = { y: 3, z: 4 };
const source5 = { y: 5 };
assign(target3, source4, source5);
// Result: { x: 1, y: 5, z: 4 } (y is overwritten with the last value)
This function only copies own properties of objects, not inherited properties. It also has an optimization that doesn't overwrite if values are the same.
target (any): The target object to which properties will be copied....sources (any[]): The source objects from which properties will be copied.(any): Returns the modified target object. The target object itself is modified and returned.