fast-copy

fast-copy

A blazing fast deep object copier

Table of contents

• fast-copy
  • Table of contents
  • Usage
  • Options
    • isStrict
    • maxDepth
    • 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));

maxDepth

The maximum number of nested objects traversed before a MaxDepthExceededError is thrown. Defaults to 1000.

Because copying is recursive, a value nested more deeply than the JavaScript engine's call stack allows will exhaust the stack. The default limit sits below that threshold, so deeply-nested values fail with a descriptive, catchable error instead of a raw RangeError.

try {
  copy(untrustedPayload);
} catch (error) {
  if (error instanceof copy.MaxDepthExceededError) {
    // `error.maxDepth` is the limit that was exceeded
  }
}

MaxDepthExceededError extends RangeError, so existing handling of the native stack-exhaustion error continues to work. In legacy environments without Object.setPrototypeOf, instanceof copy.MaxDepthExceededError cannot be supported; check error.name === 'MaxDepthExceededError' or error instanceof RangeError instead.

If you copy values that are legitimately nested more deeply, raise the limit; pass Infinity to remove it entirely, in which case sufficiently-deep values will again throw a native RangeError.

console.log(copy(deeplyNestedObject, { maxDepth: 2000 }));

NOTE: The depth counts nested objects only. Primitives and values already copied (circular references) do not contribute to it.

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
• Blob
• 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

	Operations / second
fast-copy	2,692,822
clone	1,420,277
lodash.cloneDeep	1,277,213
fast-deepclone	768,982
ramda	719,948
fast-clone	567,342
deepclone	509,547
fast-copy (strict)	420,804

Complex objects

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

	Operations / second
fast-copy	109,352
fast-deepclone	101,808
ramda	93,103
deepclone	74,270
fast-clone	49,911
clone	46,355
lodash.cloneDeep	43,900
fast-copy (strict)	33,440

Big data

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

	Operations / second
fast-copy	123
fast-deepclone	101
fast-clone	93
lodash.cloneDeep	92
deepclone	66
clone	50
fast-copy (strict)	42
ramda	5

Circular objects

Objects that deeply reference themselves

	Operations / second
fast-copy	1,143,074
ramda	750,430
clone	722,632
lodash.cloneDeep	580,005
deepclone	490,824
fast-deepclone	446,585
fast-copy (strict)	321,678
fast-clone (not supported)	0

Special objects

Custom constructors, React components, etc

	Operations / second
fast-copy	78,422
clone	52,165
lodash.cloneDeep	39,648
ramda	32,372
fast-deepclone	27,518
fast-clone	27,495
deepclone	16,552
fast-copy (strict)	12,509

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

Similar packages

Other packages similar to fast-copy

lodash.clonedeep

Lodash's clonedeep method provides deep cloning functionality. It is part of the larger Lodash library, which is a general utility library. Compared to fast-copy, lodash.clonedeep may be slower but is part of a well-established utility library with a wide range of functions.

clone

The clone package offers deep cloning of objects and arrays. It is less focused on performance compared to fast-copy and does not handle some of the more complex data types that fast-copy can.

deep-copy

Deep-copy is another package that provides deep cloning capabilities. It is similar to fast-copy in its purpose but may not have the same performance optimizations.

rfdc

The rfdc (Really Fast Deep Clone) package is a competitor to fast-copy, focusing on performance for deep cloning. It claims to be faster than other deep cloning libraries for certain use cases and is a good alternative to consider when performance is critical.