A blazing fast deep object copier

fast-copy

A blazing fast deep object copier

Table of contents

• fast-copy
  • Table of contents
  • Usage
  • Options
    • isStrict
    • realm
  • Types supported
  • Benchmarks
    • Simple objects
    • Complex objects
    • Big data
    • 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

Options

isStrict

Starting in 2.0.0, you can use the isStrict option to copy the object based on strict standards, meaning:

• Properties retain their original property descriptor
• Non-enumerable properties are copied
• Non-standard properties (e.g., keys on an Array object) are copied

This is significantly slower, so you should only use this if you believe it necessary.

console.log(copy(object, { isStrict: true }));

NOTE: This option is also aliased as copy.strict.

console.log(copy.strict(object));

realm

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 realm in options, 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, { realm: 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

Big data

Very large number of properties with high amount of nesting, mainly objects and arrays

Circular objects

Objects that deeply reference themselves

Special objects

Custom constructors, React components, etc

Development

Standard practice, clone the repo and yarn (or 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 rimraf on the dist 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
• prepublishOnly => run lint, test:coverage, and dist scripts
• release => run prepublishOnly and release with new version
• release:beta => run prepublishOnly and release with new beta version
• release:dry => run prepublishOnly and simulate a new release
• 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