assignIn (Lodash compatibility)

Use Object.assign instead

This assignIn function operates slowly due to additional processing for copying inherited properties and value comparison logic.

Use the faster and more modern Object.assign instead.

Assigns all properties (including inherited properties) from source objects to a target object.

const result = assignIn(target, ...sources);

Usage

assignIn(target, ...sources)

Use assignIn when you want to copy both own and inherited properties from source objects to a target object. Unlike assign, it includes properties from the prototype chain.

import { assignIn } from 'es-toolkit/compat';

// Basic usage
const target = { a: 1, b: 2 };
const source = { b: 3, c: 4 };
const result = assignIn(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 };
assignIn(target2, source1, source2);
// Result: { a: 1, b: 2, c: 3 }

// Copying inherited properties too
function Parent() {}
Parent.prototype.inherited = 'inheritedValue';
const child = Object.create(Parent.prototype);
child.own = 'ownValue';

const target3 = {};
assignIn(target3, child);
// Result: { own: 'ownValue', inherited: 'inheritedValue' }

// Also copies array index properties and length
const arr = [1, 2, 3];
arr.customProp = 'custom';
const target4 = {};
assignIn(target4, arr);
// Result: { '0': 1, '1': 2, '2': 3, customProp: 'custom' }

Unlike assign, this function copies inherited properties as well. It also has an optimization that doesn't overwrite if values are the same.

Parameters

• target (any): The target object to which properties will be copied.
• ...sources (any[]): The source objects from which properties will be copied. Both own and inherited properties are copied.

Returns

(any): Returns the modified target object. The target object itself is modified and returned.