fast-equals

What is fast-equals?

The fast-equals package is a high-performance deep equality checking library that provides functions to determine if two values are deeply equal. It is optimized for speed and can handle complex data structures, including objects, arrays, dates, and more.

What are fast-equals's main functionalities?

deepEqual

Checks if two values are deeply equal, meaning all their nested properties are equal.

const { deepEqual } = require('fast-equals');
console.log(deepEqual({ foo: 'bar' }, { foo: 'bar' })); // true

shallowEqual

Checks if two values are shallowly equal, meaning their immediate properties are equal without checking nested objects.

const { shallowEqual } = require('fast-equals');
console.log(shallowEqual({ foo: 'bar' }, { foo: 'bar' })); // true

circularDeepEqual

Checks if two values are deeply equal, including when they have circular references.

const { circularDeepEqual } = require('fast-equals');
const objectA = { foo: 'bar' };
objectA.self = objectA;
const objectB = { foo: 'bar' };
objectB.self = objectB;
console.log(circularDeepEqual(objectA, objectB)); // true

circularShallowEqual

Checks if two values are shallowly equal, including when they have circular references.

const { circularShallowEqual } = require('fast-equals');
const arrayA = ['foo', 'bar'];
arrayA.push(arrayA);
const arrayB = ['foo', 'bar'];
arrayB.push(arrayB);
console.log(circularShallowEqual(arrayA, arrayB)); // true

sameValueZeroEqual

Checks if two values are equal according to the SameValueZero comparison algorithm, which treats NaN as equal to NaN and -0 as equal to +0.

const { sameValueZeroEqual } = require('fast-equals');
console.log(sameValueZeroEqual(NaN, NaN)); // true

Other packages similar to fast-equals

lodash.isequal

Lodash's isEqual function is a popular utility for performing deep equality checks. It is part of the larger Lodash library, which offers a wide range of utilities for working with arrays, objects, and other data types. Compared to fast-equals, lodash.isequal may be slower but is part of a well-established utility library with a large user base.

deep-equal

The deep-equal package provides functions for deep equality checking. It is less optimized for performance compared to fast-equals but offers a simple API for checking deep equality between two values.

ramda

Ramda is a functional programming library that includes a deep equality checking function called equals. Ramda's approach is more functional and immutable compared to fast-equals, and it is designed to work well in a functional programming context.

README

fast-equals

Perform blazing fast equality comparisons (either deep or shallow) on two objects passed, while also maintaining a high degree of flexibility for various implementation use-cases. It has no dependencies, and is ~1.8kB when minified and gzipped.

The following types are handled out-of-the-box:

• Plain objects (including react elements and Arguments)
• Arrays
• Typed Arrays
• Date objects
• RegExp objects
• Map / Set iterables
• Promise objects
• Primitive wrappers (new Boolean() / new Number() / new String())
• Custom class instances, including subclasses of native classes

Methods are available for deep, shallow, or referential equality comparison. In addition, you can opt into support for circular objects, or performing a "strict" comparison with unconventional property definition, or both. You can also customize any specific type comparison based on your application's use-cases.

Table of contents

• fast-equals
  • Table of contents
  • Usage
    • Specific builds
  • Available methods
    • deepEqual
      • Comparing Maps
    • shallowEqual
    • sameValueZeroEqual
    • circularDeepEqual
    • circularShallowEqual
    • strictDeepEqual
    • strictShallowEqual
    • strictCircularDeepEqual
    • strictCircularShallowEqual
    • createCustomEqual
      • Recipes
  • Benchmarks
  • Development

Usage

import { deepEqual } from 'fast-equals';

console.log(deepEqual({ foo: 'bar' }, { foo: 'bar' })); // true

Specific builds

By default, npm should resolve the correct build of the package based on your consumption (ESM vs CommonJS). However, if you want to force use of a specific build, they can be located here:

• ESM => fast-equals/dist/esm/index.mjs
• CommonJS => fast-equals/dist/cjs/index.cjs
• UMD => fast-equals/dist/umd/index.js
• Minified UMD => fast-equals/dist/min/index.js

If you are having issues loading a specific build type, please file an issue.

Available methods

deepEqual

Performs a deep equality comparison on the two objects passed and returns a boolean representing the value equivalency of the objects.

import { deepEqual } from 'fast-equals';

const objectA = { foo: { bar: 'baz' } };
const objectB = { foo: { bar: 'baz' } };

console.log(objectA === objectB); // false
console.log(deepEqual(objectA, objectB)); // true

Comparing Maps

Map objects support complex keys (objects, Arrays, etc.), however the spec for key lookups in Map are based on SameZeroValue. If the spec were followed for comparison, the following would always be false:

const mapA = new Map([[{ foo: 'bar' }, { baz: 'quz' }]]);
const mapB = new Map([[{ foo: 'bar' }, { baz: 'quz' }]]);

deepEqual(mapA, mapB);

To support true deep equality of all contents, fast-equals will perform a deep equality comparison for key and value parirs. Therefore, the above would be true.

shallowEqual

Performs a shallow equality comparison on the two objects passed and returns a boolean representing the value equivalency of the objects.

import { shallowEqual } from 'fast-equals';

const nestedObject = { bar: 'baz' };

const objectA = { foo: nestedObject };
const objectB = { foo: nestedObject };
const objectC = { foo: { bar: 'baz' } };

console.log(objectA === objectB); // false
console.log(shallowEqual(objectA, objectB)); // true
console.log(shallowEqual(objectA, objectC)); // false

sameValueZeroEqual

Performs a SameValueZero comparison on the two objects passed and returns a boolean representing the value equivalency of the objects. In simple terms, this means either strictly equal or both NaN.

import { sameValueZeroEqual } from 'fast-equals';

const mainObject = { foo: NaN, bar: 'baz' };

const objectA = 'baz';
const objectB = NaN;
const objectC = { foo: NaN, bar: 'baz' };

console.log(sameValueZeroEqual(mainObject.bar, objectA)); // true
console.log(sameValueZeroEqual(mainObject.foo, objectB)); // true
console.log(sameValueZeroEqual(mainObject, objectC)); // false

circularDeepEqual

Performs the same comparison as deepEqual but supports circular objects. It is slower than deepEqual, so only use if you know circular objects are present.

function Circular(value) {
  this.me = {
    deeply: {
      nested: {
        reference: this,
      },
    },
    value,
  };
}

console.log(circularDeepEqual(new Circular('foo'), new Circular('foo'))); // true
console.log(circularDeepEqual(new Circular('foo'), new Circular('bar'))); // false

Just as with deepEqual, both keys and values are compared for deep equality.

circularShallowEqual

Performs the same comparison as shallowequal but supports circular objects. It is slower than shallowEqual, so only use if you know circular objects are present.

const array = ['foo'];

array.push(array);

console.log(circularShallowEqual(array, ['foo', array])); // true
console.log(circularShallowEqual(array, [array])); // false

strictDeepEqual

Performs the same comparison as deepEqual but performs a strict comparison of the objects. In this includes:

• Checking symbol properties
• Checking non-enumerable properties in object comparisons
• Checking full descriptor of properties on the object to match
• Checking non-index properties on arrays
• Checking non-key properties on Map / Set objects

const array = [{ foo: 'bar' }];
const otherArray = [{ foo: 'bar' }];

array.bar = 'baz';
otherArray.bar = 'baz';

console.log(strictDeepEqual(array, otherArray)); // true;
console.log(strictDeepEqual(array, [{ foo: 'bar' }])); // false;

strictShallowEqual

Performs the same comparison as shallowEqual but performs a strict comparison of the objects. In this includes:

• Checking non-enumerable properties in object comparisons
• Checking full descriptor of properties on the object to match
• Checking non-index properties on arrays
• Checking non-key properties on Map / Set objects

const array = ['foo'];
const otherArray = ['foo'];

array.bar = 'baz';
otherArray.bar = 'baz';

console.log(strictDeepEqual(array, otherArray)); // true;
console.log(strictDeepEqual(array, ['foo'])); // false;

strictCircularDeepEqual

Performs the same comparison as circularDeepEqual but performs a strict comparison of the objects. In this includes:

• Checking Symbol properties on the object
• Checking non-enumerable properties in object comparisons
• Checking full descriptor of properties on the object to match
• Checking non-index properties on arrays
• Checking non-key properties on Map / Set objects

function Circular(value) {
  this.me = {
    deeply: {
      nested: {
        reference: this,
      },
    },
    value,
  };
}

const first = new Circular('foo');

Object.defineProperty(first, 'bar', {
  enumerable: false,
  value: 'baz',
});

const second = new Circular('foo');

Object.defineProperty(second, 'bar', {
  enumerable: false,
  value: 'baz',
});

console.log(circularDeepEqual(first, second)); // true
console.log(circularDeepEqual(first, new Circular('foo'))); // false

strictCircularShallowEqual

Performs the same comparison as circularShallowEqual but performs a strict comparison of the objects. In this includes:

• Checking non-enumerable properties in object comparisons
• Checking full descriptor of properties on the object to match
• Checking non-index properties on arrays
• Checking non-key properties on Map / Set objects

const array = ['foo'];
const otherArray = ['foo'];

array.push(array);
otherArray.push(otherArray);

array.bar = 'baz';
otherArray.bar = 'baz';

console.log(circularShallowEqual(array, otherArray)); // true
console.log(circularShallowEqual(array, ['foo', array])); // false

createCustomEqual

Creates a custom equality comparator that will be used on nested values in the object. Unlike deepEqual and shallowEqual, this is a factory method that receives the default options used internally, and allows you to override the defaults as needed. This is generally for extreme edge-cases, or supporting legacy environments.

The signature is as follows:

interface Cache<Key extends object, Value> {
  delete(key: Key): boolean;
  get(key: Key): Value | undefined;
  set(key: Key, value: any): any;
}

interface ComparatorConfig<Meta> {
  areArraysEqual: TypeEqualityComparator<any[], Meta>;
  areDatesEqual: TypeEqualityComparator<Date, Meta>;
  areErrorsEqual: TypeEqualityComparator<Error, Meta>;
  areFunctionsEqual: TypeEqualityComparator<(...args: any[]) => any, Meta>;
  areMapsEqual: TypeEqualityComparator<Map<any, any>, Meta>;
  areObjectsEqual: TypeEqualityComparator<Record<string, any>, Meta>;
  arePrimitiveWrappersEqual: TypeEqualityComparator<
    boolean | string | number,
    Meta
  >;
  areRegExpsEqual: TypeEqualityComparator<RegExp, Meta>;
  areSetsEqual: TypeEqualityComparator<Set<any>, Meta>;
  areTypedArraysEqual: TypeEqualityComparatory<TypedArray, Meta>;
  areUrlsEqual: TypeEqualityComparatory<URL, Meta>;
}

function createCustomEqual<Meta>(options: {
  circular?: boolean;
  createCustomConfig?: (
    defaultConfig: ComparatorConfig<Meta>,
  ) => Partial<ComparatorConfig<Meta>>;
  createInternalComparator?: (
    compare: <A, B>(a: A, b: B, state: State<Meta>) => boolean,
  ) => (
    a: any,
    b: any,
    indexOrKeyA: any,
    indexOrKeyB: any,
    parentA: any,
    parentB: any,
    state: State<Meta>,
  ) => boolean;
  createState?: () => { cache?: Cache; meta?: Meta };
  strict?: boolean;
}): <A, B>(a: A, b: B) => boolean;

Create a custom equality comparator. This allows complete control over building a bespoke equality method, in case your use-case requires a higher degree of performance, legacy environment support, or any other non-standard usage. The recipes provide examples of use in different use-cases, but if you have a specific goal in mind and would like assistance feel free to file an issue.

NOTE: Map implementations compare equality for both keys and value. When using a custom comparator and comparing equality of the keys, the iteration index is provided as both indexOrKeyA and indexOrKeyB to help use-cases where ordering of keys matters to equality.

Recipes

Some recipes have been created to provide examples of use-cases for createCustomEqual. Even if not directly applicable to the problem you are solving, they can offer guidance of how to structure your solution.

• Legacy environment support for RegExp comparators
• Explicit property check
• Using meta in comparison
• Comparing non-standard properties
• Strict property descriptor comparison
• Legacy environment support for circualr equal comparators

Benchmarks

All benchmarks were performed on an i9-11900H Ubuntu Linux 24.04 laptop with 64GB of memory using NodeJS version 20.17.0, and are based on averages of running comparisons based deep equality on the following object types:

• Primitives (String, Number, null, undefined)
• Function
• Object
• Array
• Date
• RegExp
• react elements
• A mixed object with a combination of all the above types

Testing mixed objects equal...
┌─────────┬─────────────────────────────────┬────────────────┐
│ (index) │ Package                         │ Ops/sec        │
├─────────┼─────────────────────────────────┼────────────────┤
│ 0       │ 'fast-equals'                   │ 1256867.529926 │
│ 1       │ 'fast-deep-equal'               │ 1207041.997437 │
│ 2       │ 'shallow-equal-fuzzy'           │ 1142536.391324 │
│ 3       │ 'react-fast-compare'            │ 1140373.249605 │
│ 4       │ 'dequal/lite'                   │ 708240.354044  │
│ 5       │ 'dequal'                        │ 704655.931143  │
│ 6       │ 'fast-equals (circular)'        │ 595853.718756  │
│ 7       │ 'underscore.isEqual'            │ 433596.570863  │
│ 8       │ 'assert.deepStrictEqual'        │ 310595.198662  │
│ 9       │ 'lodash.isEqual'                │ 232192.454526  │
│ 10      │ 'fast-equals (strict)'          │ 175941.250843  │
│ 11      │ 'fast-equals (strict circular)' │ 154606.328398  │
│ 12      │ 'deep-eql'                      │ 136052.484375  │
│ 13      │ 'deep-equal'                    │ 854.061311     │
└─────────┴─────────────────────────────────┴────────────────┘

Testing mixed objects not equal...
┌─────────┬─────────────────────────────────┬────────────────┐
│ (index) │ Package                         │ Ops/sec        │
├─────────┼─────────────────────────────────┼────────────────┤
│ 0       │ 'fast-equals'                   │ 3795307.779634 │
│ 1       │ 'fast-deep-equal'               │ 2987150.35694  │
│ 2       │ 'react-fast-compare'            │ 2733075.404272 │
│ 3       │ 'fast-equals (circular)'        │ 2311547.685659 │
│ 4       │ 'dequal/lite'                   │ 1156909.54415  │
│ 5       │ 'dequal'                        │ 1151209.161878 │
│ 6       │ 'fast-equals (strict)'          │ 1102248.247412 │
│ 7       │ 'fast-equals (strict circular)' │ 1020639.089577 │
│ 8       │ 'nano-equal'                    │ 1009557.685012 │
│ 9       │ 'underscore.isEqual'            │ 770286.698227  │
│ 10      │ 'lodash.isEqual'                │ 296338.570457  │
│ 11      │ 'deep-eql'                      │ 152741.182224  │
│ 12      │ 'assert.deepStrictEqual'        │ 20163.203513   │
│ 13      │ 'deep-equal'                    │ 3519.448516    │
└─────────┴─────────────────────────────────┴────────────────┘

Caveats that impact the benchmark (and accuracy of comparison):

• Maps, Promises, and Sets were excluded from the benchmark entirely because no library other than deep-eql fully supported their comparison
• fast-deep-equal, react-fast-compare and nano-equal throw on objects with null as prototype (Object.create(null))
• assert.deepStrictEqual does not support NaN or SameValueZero equality for dates
• deep-eql does not support SameValueZero equality for zero equality (positive and negative zero are not equal)
• deep-equal does not support NaN and does not strictly compare object type, or date / regexp values, nor uses SameValueZero equality for dates
• fast-deep-equal does not support NaN or SameValueZero equality for dates
• nano-equal does not strictly compare object property structure, array length, or object type, nor SameValueZero equality for dates
• react-fast-compare does not support NaN or SameValueZero equality for dates, and does not compare function equality
• shallow-equal-fuzzy does not strictly compare object type or regexp values, nor SameValueZero equality for dates
• underscore.isEqual does not support SameValueZero equality for primitives or dates

All of these have the potential of inflating the respective library's numbers in comparison to fast-equals, but it was the closest apples-to-apples comparison I could create of a reasonable sample size. It should be noted that react elements can be circular objects, however simple elements are not; I kept the react comparison very basic to allow it to be included.

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 main, module, and browser distributables with rollup
• clean => run rimraf on the dist folder
• dev => start webpack playground App
• dist => run build
• 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

Changelog

5.2.2

• #139 - Add file extensions to type definition files to allow it to work in projects with NodeNext module resolution