deepmerge-ts

What is deepmerge-ts?

The deepmerge-ts package is a TypeScript library designed to deeply merge two or more objects. It ensures type safety and is particularly useful for complex nested objects where shallow merging would not suffice.

What are deepmerge-ts's main functionalities?

Basic Deep Merge

This feature allows you to deeply merge two objects. In this example, obj1 and obj2 are merged such that the nested properties are combined.

const deepmerge = require('deepmerge-ts').default;
const obj1 = { a: 1, b: { c: 2 } };
const obj2 = { b: { d: 3 } };
const result = deepmerge(obj1, obj2);
console.log(result); // { a: 1, b: { c: 2, d: 3 } }

Array Merge

This feature allows you to merge arrays within objects. In this example, the arrays in obj1 and obj2 are concatenated.

const deepmerge = require('deepmerge-ts').default;
const obj1 = { a: [1, 2, 3] };
const obj2 = { a: [4, 5] };
const result = deepmerge(obj1, obj2);
console.log(result); // { a: [1, 2, 3, 4, 5] }

Custom Merge Function

This feature allows you to define custom merge functions for specific keys. In this example, the custom merge function concatenates arrays for the key 'a'.

const deepmerge = require('deepmerge-ts').default;
const customMerge = (key, options) => {
  if (key === 'a') {
    return (a, b) => a.concat(b);
  }
  return undefined;
};
const obj1 = { a: [1, 2, 3], b: { c: 2 } };
const obj2 = { a: [4, 5], b: { d: 3 } };
const result = deepmerge(obj1, obj2, { customMerge });
console.log(result); // { a: [1, 2, 3, 4, 5], b: { c: 2, d: 3 } }

Other packages similar to deepmerge-ts

deepmerge

The deepmerge package is a popular library for deep merging objects in JavaScript. It is similar to deepmerge-ts but does not provide TypeScript type safety out of the box.

lodash.merge

Lodash is a utility library that offers a wide range of functions, including deep merging with lodash.merge. While it is versatile and widely used, it is a larger library compared to deepmerge-ts, which is more specialized.

merge-deep

The merge-deep package is another library for deep merging objects. It is simpler and less feature-rich compared to deepmerge-ts, focusing solely on deep merging without additional customization options.

README

DeepmergeTS

Deeply merge 2 or more objects respecting type information.

Donate

Any donations would be much appreciated. 😄

Enterprise Users

deepmerge-ts is available as part of the Tidelift Subscription.

Tidelift is working with the maintainers of deepmerge-ts and a growing network of open source maintainers to ensure your open source software supply chain meets enterprise standards now and into the future. Learn more.

Installation

npm

# Install with npm
npm install deepmerge-ts

# Install with pnpm
pnpm add deepmerge-ts

# Install with yarn
yarn add deepmerge-ts

# Install with bun
bun add deepmerge-ts

jsr

# Install in a node project
npx jsr add @rebeccastevens/deepmerge

# Install in a deno project
deno add jsr:@rebeccastevens/deepmerge

# Install in a bun project
bunx jsr add @rebeccastevens/deepmerge

Features

• Smart merging - High performance.
• Merged output has correct typing.
• Record merging support.
• Array merging support.
• Map and Set merging support.
• Customized merging.

Usage

Example using default config

import { deepmerge } from "deepmerge-ts";

const x = {
  record: {
    prop1: "value1",
    prop2: "value2",
  },
  array: [1, 2, 3],
  set: new Set([1, 2, 3]),
  map: new Map([
    ["key1", "value1"],
    ["key2", "value2"],
  ]),
};

const y = {
  record: {
    prop1: "changed",
    prop3: "value3",
  },
  array: [2, 3, 4],
  set: new Set([2, 3, 4]),
  map: new Map([
    ["key2", "changed"],
    ["key3", "value3"],
  ]),
};

const z = {
  record: {
    prop1: undefined,
    prop3: undefined,
    prop2: undefined,
    prop4: undefined,
  },
  array: undefined,
  set: undefined,
  map: undefined,
};

const merged = deepmerge(x, y, z);

console.log(merged);

// Prettierfied output:
//
// Object {
//   "record": Object {
//     "prop1": "changed",
//     "prop2": "value2",
//     "prop3": "value3",
//     "prop4": undefined,
//   },
//   "array": Array [1, 2, 3, 2, 3, 4],
//   "set": Set { 1, 2, 3, 4 },
//   "map": Map {
//     "key1" => "value1",
//     "key2" => "changed",
//     "key3" => "value3",
//   },
// }

You can try out this example at codesandbox.io.

Merging into a Target

You can use deepmergeInto if you want to update a target object with the merge result instead of creating a new object.

This function is best used with objects that are all of the same type.

Note: If the target object's type differs from the input objects, we'll assert that the target's type has changed (this is not done automatically with deepmergeIntoCustom).

Customized the Merging Process

We provide a customizer function for each of our main deepmerge functions: deepmergeCustom and deepmergeIntoCustom. You can use these to customize the details of how values should be merged together.

See deepmerge custom docs for more details.

Performance

We use smart merging instead of the classic merging strategy which some alternative libraries use. This vastly improves performance, both in execution time and memory usage.

Classic Merge (not what we do)

With classic merging, each input is merged with the next input until all inputs are merged.

This strategy has large performance issues when lots of items need to be merged.

Smart Merge (what we do)

With our smart merging, we look ahead to see what can be merged and only merge those things.

In addition to performance improvements, this strategy merges multiple inputs at once; allowing for benefits such as taking averages of the inputs.

API

See API docs.