benchmarks

V8
{
  'react:equal:monomorphic': { average: 1206.33, stddev: 59.63406930792349 },
  'react:unequal:monomorphic': { average: 1198.67, stddev: 41.51572660517404 },
  'hughsk/shallow-equals:equal:monomorphic': { average: 595.33, stddev: 33.47967874530592 },
  'hughsk/shallow-equals:unequal:monomorphic': { average: 559.33, stddev: 1.699673171197595 },
  'romgrk-fastCompareUnsafe:equal:monomorphic': { average: 510.33, stddev: 1.247219128924647 },
  'romgrk-fastCompareUnsafe:unequal:monomorphic': { average: 447.67, stddev: 2.0548046676563256 },
  'romgrk-fastCompareStrict:equal:monomorphic': { average: 881.33, stddev: 1.699673171197595 },
  'romgrk-fastCompareStrict:unequal:monomorphic': { average: 775.33, stddev: 0.9428090415820634 },
  'romgrk-fastCompare:equal:monomorphic': { average: 892.33, stddev: 4.714045207910316 },
  'romgrk-fastCompare:unequal:monomorphic': { average: 787.67, stddev: 4.642796092394706 }
}

JSC
{
  "react:equal:monomorphic": { average: 401, stddev: 25.152865973217974, },
  "react:unequal:monomorphic": { average: 415.33, stddev: 3.39934634239519, },
  "hughsk/shallow-equals:equal:monomorphic": { average: 297, stddev: 14.236104336041748, },
  "hughsk/shallow-equals:unequal:monomorphic": { average: 189.33, stddev: 2.0548046676563256, },
  "romgrk-fastCompareUnsafe:equal:monomorphic": { average: 313.67, stddev: 30.26916289265731, },
  "romgrk-fastCompareUnsafe:unequal:monomorphic": { average: 244.67, stddev: 3.8586123009300755, },
  "romgrk-fastCompareStrict:equal:monomorphic": { average: 199.67, stddev: 6.847546194724712, },
  "romgrk-fastCompareStrict:unequal:monomorphic": { average: 128.67, stddev: 1.247219128924647, },
  "romgrk-fastCompare:equal:monomorphic": { average: 293, stddev: 27.067816067549053, },
  "romgrk-fastCompare:unequal:monomorphic": { average: 236, stddev: 1.4142135623730951, },
}

SpiderMonkey
{
    "react:equal:monomorphic": { "average": 975.33, "stddev": 1.247219128924647 },
    "react:unequal:monomorphic": { "average": 1073, "stddev": 13.490737563232042 },
    "hughsk/shallow-equals:equal:monomorphic": { "average": 661.33, "stddev": 50.54590872552287 },
    "hughsk/shallow-equals:unequal:monomorphic": { "average": 509, "stddev": 22.015146301277824 },
    "romgrk-fastCompareUnsafe:equal:monomorphic": { "average": 468.33, "stddev": 6.182412330330469 },
    "romgrk-fastCompareUnsafe:unequal:monomorphic": { "average": 466.67, "stddev": 3.091206165165235 },
    "romgrk-fastCompareStrict:equal:monomorphic": { "average": 506.33, "stddev": 3.39934634239519 },
    "romgrk-fastCompareStrict:unequal:monomorphic": { "average": 503.67, "stddev": 3.6817870057290873 },
    "romgrk-fastCompare:equal:monomorphic": { "average": 495.67, "stddev": 13.474255287605157 },
    "romgrk-fastCompare:unequal:monomorphic": { "average": 481, "stddev": 2.160246899469287 }
}

strict-safe-unsafe.ts

import { memo } from 'react'
const is = Object.is;

export default fastMemo;

export function fastMemo<T>(component: T): T {
  return memo(component as any, fastCompare) as unknown as T;
}

export function fastMemoUnsafe<T>(component: T): T {
  return memo(component as any, fastCompareUnsafe) as unknown as T;
}

export function fastMemoStrict<T>(component: T): T {
  return memo(component as any, fastCompareStrict) as unknown as T;
}

export function fastCompareStrict<T extends Record<string, any> | null>(a: T, b: T) {
  if (a === b) {
    return true;
  }
  if (!(a instanceof Object) || !(b instanceof Object)) {
    return false;
  }

  let aLength = 0;
  let bLength = 0;

  for (const key in a) {
    aLength += 1;

    if (!is(a[key], b[key])) {
      return false;
    }
    if (!(key in b)) {
      return false;
    }
  }

  for (const _ in b) {
    bLength += 1;
  }

  return aLength === bLength;
}

export function fastCompare<T extends Record<string, any>>(a: T, b: T) {
  let aLength = 0;
  let bLength = 0;

  for (const key in a) {
    aLength += 1;

    if (!is(a[key], b[key])) {
      return false;
    }
    if (!(key in b)) {
      return false;
    }
  }

  for (const _ in b) {
    bLength += 1;
  }

  return aLength === bLength;
}

export function fastCompareUnsafe<T extends Record<string, any>>(a: T, b: T) {
  let aLength = 0;
  let bLength = 0;

  for (const key in a) {
    aLength += 1;

    if (!is(a[key], b[key])) {
      return false;
    }
  }

  for (const _ in b) {
    bLength += 1;
  }

  return aLength === bLength;
}