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https://github.com/planttheidea/fast-equals

A blazing fast equality comparison, either shallow or deep
https://github.com/planttheidea/fast-equals

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A blazing fast equality comparison, either shallow or deep

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README 

        
# fast-equals










Perform [blazing fast](#benchmarks) 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](#fast-equals)

  - [Table of contents](#table-of-contents)

  - [Usage](#usage)

    - [Specific builds](#specific-builds)

  - [Available methods](#available-methods)

    - [deepEqual](#deepequal)

      - [Comparing `Map`s](#comparing-maps)

    - [shallowEqual](#shallowequal)

    - [sameValueZeroEqual](#samevaluezeroequal)

    - [circularDeepEqual](#circulardeepequal)

    - [circularShallowEqual](#circularshallowequal)

    - [strictDeepEqual](#strictdeepequal)

    - [strictShallowEqual](#strictshallowequal)

    - [strictCircularDeepEqual](#strictcirculardeepequal)

    - [strictCircularShallowEqual](#strictcircularshallowequal)

    - [createCustomEqual](#createcustomequal)

      - [Recipes](#recipes)

  - [Benchmarks](#benchmarks)

  - [Development](#development)



## Usage



```ts

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](https://github.com/planttheidea/fast-equals/issues).



## Available methods



### deepEqual



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



```ts

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 `Map`s



`Map` objects support complex keys (objects, Arrays, etc.), however [the spec for key lookups in `Map` are based on `SameZeroValue`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map#key_equality). If the spec were followed for comparison, the following would always be `false`:



```ts

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.



```ts

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`](http://ecma-international.org/ecma-262/7.0/#sec-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`.



```ts

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.



```ts

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](#comparing-maps).



### 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.



```ts

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



```ts

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



```ts

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



```ts

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



```ts

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:



```ts

interface Cache {

  delete(key: Key): boolean;

  get(key: Key): Value | undefined;

  set(key: Key, value: any): any;

}



interface ComparatorConfig {

  areArraysEqual: TypeEqualityComparator;

  areDatesEqual: TypeEqualityComparator;

  areMapsEqual: TypeEqualityComparator, Meta>;

  areObjectsEqual: TypeEqualityComparator, Meta>;

  arePrimitiveWrappersEqual: TypeEqualityComparator<

    boolean | string | number,

    Meta

  >;

  areRegExpsEqual: TypeEqualityComparator;

  areSetsEqual: TypeEqualityComparator, Meta>;

  areTypedArraysEqual: TypeEqualityComparatory;

}



function createCustomEqual(options: {

  circular?: boolean;

  createCustomConfig?: (

    defaultConfig: ComparatorConfig,

  ) => Partial>;

  createInternalComparator?: (

    compare: (a: A, b: B, state: State) => boolean,

  ) => (

    a: any,

    b: any,

    indexOrKeyA: any,

    indexOrKeyB: any,

    parentA: any,

    parentB: any,

    state: State,

  ) => boolean;

  createState?: () => { cache?: Cache; meta?: Meta };

  strict?: boolean;

}): (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](#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](https://github.com/planttheidea/fast-equals/issues).



_**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](./recipes/legacy-regexp-support.md)

- [Explicit property check](./recipes/explicit-property-check.md)

- [Using `meta` in comparison](./recipes//using-meta-in-comparison.md)

- [Comparing non-standard properties](./recipes/non-standard-properties.md)

- [Strict property descriptor comparison](./recipes/strict-property-descriptor-check.md)

- [Legacy environment support for circualr equal comparators](./recipes/legacy-circular-equal-support.md)



## 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:



- Primitives (`String`, `Number`, `null`, `undefined`)

- `Function`

- `Object`

- `Array`

- `Date`

- `RegExp`

- `react` elements

- A mixed object with a combination of all the above types



```bash

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):



- `Map`s, `Promise`s, and `Set`s 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