fast-copy

A blazing fast deep object copier

Table of contents

• fast-copy
  • Table of contents
  • Usage
  • API
    • copy
    • copyStrict
  • Types supported
  • Aspects of copying
    • Error references are copied over (instead of creating a new *Error object)
    • The constructor of the original object is used, instead of using known globals.
  • 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

API

copy

Deeply copy the object passed.

import { copy } from 'fast-copy';

const copied = copy({ foo: 'bar' });

copyStrict

Deeply copy the object passed, but with additional strictness when replicating the original object:

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

import { copyStrict } from 'fast-copy';

const object = { foo: 'bar' };
object.nonEnumerable = Object.defineProperty(object, 'bar', {
  enumerable: false,
  value: 'baz',
});

const copied = copy(object);

NOTE: This method is significantly slower than copy, so it is recommended to only use this when you have specific use-cases that require it.

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. By default, a cache based on WeakSet is used, but if WeakSet is not available then a fallback is used. The benchmarks quoted below are based on use of WeakSet.

Aspects of copying

Inherently, what is considered a valid copy is subjective because of different requirements and use-cases. For this library, some decisions were explicitly made.

Error references are copied over (instead of creating a new *Error object)

While it would be relatively trivial to copy over the message and stack to a new object of the same Error subclass, it is a common practice to "override" the message or stack, and copies would not retain this mutation. As such, the original reference is copied.

The constructor of the original object is used, instead of using known globals.

Starting in ES2015, native globals can be subclassed like any custom class. When copying, we explicitly reuse the constructor of the original object. However, the expectation is that these subclasses would have the same constructur signature as their native base class. This is a common community practice, however because there is the possibility of inaccuracy if the contract differs, it should be noted.

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 => run build:files and build:types
• build:files => build dist files with rollup
• build:types => build TypeScript types for consumers
• 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