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planttheidea / fast-equals

A blazing fast equality comparison, either shallow or deep
MIT License
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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:

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

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:

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:

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:

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:

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:

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>;
  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>;
}

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.

Benchmarks

All benchmarks were performed on an i9-11900H Ubuntu Linux 22.04 laptop with 64GB of memory using NodeJS version 16.14.2, and are based on averages of running comparisons based deep equality on the following object types:

Testing mixed objects equal...
┌─────────┬─────────────────────────────────┬────────────────┐
│ (index) │             Package             │    Ops/sec     │
├─────────┼─────────────────────────────────┼────────────────┤
│    0    │          'fast-equals'          │ 1249567.730326 │
│    1    │        'fast-deep-equal'        │ 1182463.587514 │
│    2    │      'react-fast-compare'       │ 1152487.319161 │
│    3    │      'shallow-equal-fuzzy'      │ 1092360.712389 │
│    4    │    'fast-equals (circular)'     │  676669.92003  │
│    5    │      'underscore.isEqual'       │ 429430.837497  │
│    6    │        'lodash.isEqual'         │ 237915.684734  │
│    7    │     'fast-equals (strict)'      │  181386.38032  │
│    8    │ 'fast-equals (strict circular)' │ 156779.745875  │
│    9    │           'deep-eql'            │ 139155.099209  │
│   10    │          'deep-equal'           │  1026.527229   │
└─────────┴─────────────────────────────────┴────────────────┘

Testing mixed objects not equal...
┌─────────┬─────────────────────────────────┬────────────────┐
│ (index) │             Package             │    Ops/sec     │
├─────────┼─────────────────────────────────┼────────────────┤
│    0    │          'fast-equals'          │ 3255824.097237 │
│    1    │      'react-fast-compare'       │ 2654721.726058 │
│    2    │        'fast-deep-equal'        │ 2582218.974752 │
│    3    │    'fast-equals (circular)'     │ 2474303.26566  │
│    4    │     'fast-equals (strict)'      │ 1088066.604881 │
│    5    │ 'fast-equals (strict circular)' │ 949253.614181  │
│    6    │          'nano-equal'           │ 939170.554148  │
│    7    │      'underscore.isEqual'       │ 738852.197879  │
│    8    │        'lodash.isEqual'         │ 307306.622212  │
│    9    │           'deep-eql'            │ 156250.110401  │
│   10    │    'assert.deepStrictEqual'     │  22839.454561  │
│   11    │          'deep-equal'           │   4034.45114   │
└─────────┴─────────────────────────────────┴────────────────┘

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

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: