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. It has no dependencies, and is ~1.27kB when minified and gzipped.

Unlike most equality validation libraries, the following types are handled out-of-the-box:

• NaN
• Date objects
• RegExp objects
• Map / Set iterables
• Promise objects
• react elements

Starting with version 1.5.0, circular objects are supported for both deep and shallow equality (see circularDeepEqual and circularShallowEqual). You can also create a custom nested comparator, for specific scenarios (see below).

Table of contents

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

Usage

import { deepEqual } from 'fast-equals';

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

Specific builds

There are three builds, an ESM build for modern build systems / runtimes, a CommonJS build for traditional NodeJS environments, and a UMD build for legacy implementations. The ideal one will likely be chosen for you automatically, however if you want to use a specific build you can always import it directly:

• ESM => fast-equals/dist/fast-equals.esm.js
  • For older nodejs versions that do not allow ESM with file extensions other than .mjs => fast-equals/dist/fast-equals.mjs
• CommonJS => fast-equals/dist/fast-equals.cjs.js
• UMD => fast-equals/dist/fast-equals.js
• Minified UMD => fast-equals/dist/fast-equals.min.js

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

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:

type InternalEqualityComparator = (
  a: any,
  b: any,
  indexOrKeyA: any,
  indexOrKeyB: any,
  parentA: any,
  parentB: any,
  meta: any,
) => boolean;

type TypeEqualityComparator = <Type, Meta>(
  a: Type,
  b: Type,
  isEqual: InternalEqualityComparator,
  meta: Meta,
) => boolean;

interface CreateComparatorCreatorOptions<Meta> {
  areArraysEqual: TypeEqualityComparator<any[], Meta>;
  areDatesEqual: TypeEqualityComparator<Date, Meta>;
  areMapsEqual: TypeEqualityComparator<Map<any, any>, Meta>;
  areObjectsEqual: TypeEqualityComparator<Record<string, any>, Meta>;
  areRegExpsEqual: TypeEqualityComparator<RegExp, Meta>;
  areSetsEqual: TypeEqualityComparator<Set<any>, Meta>;
  createIsNestedEqual?: (
    comparator: <A, B>(a: A, b: B, meta: Meta) => boolean,
  ) => InternalEqualityComparator;
}

function createCustomEqual(
  getComparatorOptions: (
    defaultOptions: CreateComparatorOptions,
  ) => Partial<CreateComparatorOptions>,
): EqualityComparator;

The meta parameter above is whatever you want it to be. It will be passed through to all equality checks, and is meant specifically for use with custom equality methods. For example, with the circularDeepEqual and circularShallowEqual methods, it is used to pass through a cache of processed objects. You also only need to return the override handlers; absent being provided, the defaults are used.

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

createCustomCircularEqual

Operates nearly identically to createCustomEqual, with the difference being that the meta property expected by the comparator is expected to have a WeakMap contract. This is because it is used for caching accessed objects to avoid maximum stack exceeded errors. The most common use for this method is a simple way to support circular checks for references that do not have WeakMap natively.

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 circualr equal comparators

Benchmarks

All benchmarks were performed on an i7-8650U Ubuntu Linux laptop with 24GB of memory using NodeJS version 12.19.1, 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

	Operations / second
fast-equals	153,880
fast-deep-equal	144,035
react-fast-compare	130,324
nano-equal	104,624
fast-equals (circular)	97,610
shallow-equal-fuzzy	83,946
underscore.isEqual	47,370
lodash.isEqual	25,053
deep-eql	22,146
assert.deepStrictEqual	532
deep-equal	209

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
• 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