JavaScript
A blazing fast deep object copier

fast-copy

A blazing fast deep object copier

Table of contents

• Usage
  • Multiple realms
• Types supported
• Benchmarks
  • Simple objects
  • Complex objects
  • Circular objects
  • Special objects
• Development

Usage

import copy from "fast-copy";
import { deepEqual } from "fast-equals";

const object = {
  array: [123, { deep: "value" }],
  map: new Map([["foo", {}], [{ bar: "baz" }, "quz"]])
};

const copiedObject = copy(object);

console.log(copiedObject === object); // false
console.log(deepEqual(copiedObject, object)); // true

Multiple realms

Under the hood, fast-copy uses instanceof to determine object types, which can cause false negatives when used in combination with iframe-based objects. To handle this edge case, you can pass the optional second parameter of realm to the copy method, which identifies which realm the object comes from and will use that realm to drive both comparisons and constructors for the copies.

<iframe srcdoc="<script>var arr = ['foo', 'bar'];</script>"></iframe>

const iframe = document.querySelector("iframe");
const arr = iframe.contentWindow.arr;

console.log(copy(arr, iframe.contentWindow)); // ['foo', 'bar']

Types supported

The following object types are deeply cloned when they are either properties on the object passed, or the object itself:

• Array
• ArrayBuffer
• Buffer
• DataView
• Date
• Float32Array
• Float64Array
• Int8Array
• Int16Array
• Int32Array
• Map
• Object
• RegExp
• Set
• Uint8Array
• Uint8ClampedArray
• Uint16Array
• Uint32Array
• React components
• Custom constructors

The following object types are copied directly, as they are either primitives, cannot be cloned, or the common use-case implementation does not expect cloning:

• AsyncFunction
• Boolean
• Error
• Function
• GeneratorFunction
• Number
• Null
• Promise
• String
• Symbol
• Undefined
• WeakMap
• WeakSet

Circular objects are supported out of the box as well. By default a cache based on WeakSet is used, but if WeakSet is not available then a standard Object fallback is used. The benchmarks quoted below are based on use of WeakSet.

Benchmarks

Simple objects

Small number of properties, all values are primitives

Complex objects

Large number of properties, values are a combination of primitives and complex objects

Circular objects

Objects that deeply reference themselves

Special objects

Custom constructors, React components, etc

Development

Standard practice, clone the repo and npm i to get the dependencies. The following npm scripts are available:

• benchmark => run benchmark tests against other equality libraries
• build => build dist files with rollup
• clean => run clean:dist, clean:es, and clean:lib scripts
• clean:dist => run rimraf on the dist folder
• clean:es => run rimraf on the es folder
• clean:lib => run rimraf on the lib folder
• dev => start webpack playground App
• dist => run build and build:minified scripts
• lint => run ESLint on all files in src folder (also runs on dev script)
• lint:fix => run lint script, but with auto-fixer
• prepublish:compile => run lint, test:coverage, transpile:lib, transpile:es, and dist scripts
• start => run dev
• test => run AVA with NODE_ENV=test on all files in test folder
• test:coverage => run same script as test with code coverage calculation via nyc
• test:watch => run same script as test but keep persistent watcher
• transpile:es => run Babel on all files in src folder (transpiled to es folder without transpilation of ES2015 export syntax)
• transpile:lib => run Babel on all files in src folder (transpiled to lib folder)