extendWith (Lodash compatibility)

Use Object.assign() with a custom function instead

This extendWith function is complex and slow due to handling inherited properties from the prototype chain and custom merge logic.

Use the faster and more modern Object.assign() with a custom function instead.

Copies own and inherited properties of objects to another object with custom logic.

const result = extendWith(object, source, customizer);

Reference

extendWith(object, ...sources, customizer)

Use extendWith to merge object properties with custom logic. It's similar to extend but allows you to decide how each property should be merged. This function is an alias for assignInWith.

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

// Copy properties with custom merge logic
const target = { a: 1, b: 2 };
extendWith(target, { b: 3, c: 4 }, (objValue, srcValue) => {
  return objValue === undefined ? srcValue : objValue;
});
// Returns: { a: 1, b: 2, c: 4 }

// Custom merge that concatenates arrays
const obj1 = { a: [1, 2] };
const obj2 = { a: [3, 4], b: [5, 6] };
extendWith(obj1, obj2, (objValue, srcValue) => {
  if (Array.isArray(objValue)) {
    return objValue.concat(srcValue);
  }
});
// Returns: { a: [1, 2, 3, 4], b: [5, 6] }

You can use multiple source objects.

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

extendWith({ a: 1 }, { b: 2 }, { c: 3 }, (objValue, srcValue) => srcValue * 2);
// Returns: { a: 1, b: 4, c: 6 }

Parameters

• object (any): The target object to receive properties.
• ...sources (any[]): The source objects that provide properties.
• customizer (function): The function that determines the value to assign for each property. It receives (objValue, srcValue, key, object, source).

Returns

(any): Returns the object with copied properties. The first argument object is modified.