deepmerge-ts

DeepmergeTS

Deeply merge 2 or more objects respecting type information.

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Enterprise Users

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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.
• Circular reference support.
• Security safeguards.
• Recursion depth limit (defaults to 1000) to prevent stack exhaustion.
• High-performance deepmergeFastUnsafe variants for trusted data.
• 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).

Customizing 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.

TypeScript Interfaces

Due to how TypeScript handles interfaces (microsoft/TypeScript#15300), interface types without an explicit index signature may not appear to merge correctly. For proper type inference when merging objects, use type aliases instead of interfaces.

High-Performance "FastUnsafe" Variants

For performance-critical code where inputs are trusted and non-circular, we provide high-performance variants that skip circular reference tracking, depth limits, prototype pollution safeguards, and metadata allocations:

• deepmergeFastUnsafe & deepmergeFastUnsafeCustom
• deepmergeIntoFastUnsafe & deepmergeIntoFastUnsafeCustom

[!WARNING] Only use these functions with trusted, non-circular data. Using with untrusted user data can result in security vulnerabilities such as prototype pollution and Denial of Service (DoS) from unbounded recursion / stack overflow.

See API 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.

Similar packages

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.