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    Fast Memoize.js

    :rabbit: Fastest possible memoization library
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    In computing, memoization is an optimization technique used primarily to speed up computer programs by storing the results of expensive function calls and returning the cached result when the same inputs occur again. — Wikipedia

    This library is an attempt to make the fastest possible memoization library in JavaScript that supports N arguments.


    npm install fast-memoize --save


    const memoize = require('fast-memoize')
    const fn = function (one, two, three) { /* ... */ }
    const memoized = memoize(fn)
    memoized('foo', 3, 'bar')
    memoized('foo', 3, 'bar') // Cache hit

    Custom cache

    The fastest cache is used for the running environment, but it is possible to pass a custom cache to be used.

    const memoized = memoize(fn, {
      cache: {
        create() {
          var store = {};
          return {
            has(key) { return (key in store); },
            get(key) { return store[key]; },
            set(key, value) { store[key] = value; }

    The custom cache should be an object containing a create method that returns an object implementing the following methods:

    • get
    • set
    • has

    Custom serializer

    To use a custom serializer:

    const memoized = memoize(fn, {
      serializer: customSerializer

    The serializer is a function that receives one argument and outputs a string that represents it. It has to be a deterministic algorithm meaning that, given one input, it always returns the same output.


    For an in depth explanation on how this library was created, go read this post on RisingStack.

    Below you can see a performance benchmark between some of the most popular libraries for memoization.

    To run the benchmark, clone the repo, install the dependencies and run npm run benchmark.

    git clone
    cd fast-memoize
    npm install
    npm run benchmark

    Against another git hash

    To benchmark the current code against a git hash, branch, ...

    npm run benchmark:compare 53fa9a62214e816cf8b5b4fa291c38f1d63677b9


    Rest & Default Parameters

    We check for function.length to get upfront the expected number of arguments in order to use the fastest strategy. But when rest & default parameters are being used, we don't receive the right number of arguments (see details).

    // Rest parameter example
    function multiply (multiplier, ...theArgs) {
      return (element) {
        return multiplier * element
    multiply.length // => 1
    // Default parameter example
    function divide (element, divisor = 1) {
      return divisor * element
    divide.length // => 1

    So if you use rest & default parameters, explicitly set the strategy to variadic.

    const memoizedMultiply = memoize(multiply, {
      strategy: memoize.strategies.variadic

    Function Arguments

    The default serializer uses JSON.stringify which will serialize functions as null. This means that if you are passing any functions as arguments you will get the same output regardless of whether you pass in different functions or indeed no function at all. The cache key generated will always be the same. To get around this you can give each function a unique ID and use that.

    let id = 0
    function memoizedId(x) {
      if (!x.__memoizedId) x.__memoizedId = ++id
      return { __memoizedId: x.__memoizedId }
    memoize((aFunction, foo) => {
      return aFunction.bind(foo)
    }, {
      serializer: args => {
        const argumentsWithFuncIds = Array.from(args).map(x => {
          if (typeof x === 'function') return memoizedId(x)
          return x
        return JSON.stringify(argumentsWithFuncIds)

    Credits  ·  GitHub @caiogondim  ·  Twitter @caio_gondim

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