Nascent Prototype Metaverse

    memoize-one
    TypeScript icon, indicating that this package has built-in type declarations

    6.0.0 • Public • Published

    memoize-one

    A memoization library that only caches the result of the most recent arguments.

    npm types minzip Downloads per month

    Rationale

    Unlike other memoization libraries, memoize-one only remembers the latest arguments and result. No need to worry about cache busting mechanisms such as maxAge, maxSize, exclusions and so on, which can be prone to memory leaks. A function memoized with memoize-one simply remembers the last arguments, and if the memoized function is next called with the same arguments then it returns the previous result.

    For working with promises, @Kikobeats has built async-memoize-one.

    Usage

    // memoize-one uses the default import
    import memoizeOne from 'memoize-one';
    
    function add(a, b) {
      return a + b;
    }
    const memoizedAdd = memoizeOne(add);
    
    memoizedAdd(1, 2);
    // add function: is called
    // [new value returned: 3]
    
    memoizedAdd(1, 2);
    // add function: not called
    // [cached result is returned: 3]
    
    memoizedAdd(2, 3);
    // add function: is called
    // [new value returned: 5]
    
    memoizedAdd(2, 3);
    // add function: not called
    // [cached result is returned: 5]
    
    memoizedAdd(1, 2);
    // add function: is called
    // [new value returned: 3]
    // 👇
    // While the result of `add(1, 2)` was previously cached
    // `(1, 2)` was not the *latest* arguments (the last call was `(2, 3)`)
    // so the previous cached result of `(1, 3)` was lost

    Installation

    # yarn
    yarn add memoize-one
    
    # npm
    npm install memoize-one --save

    Function argument equality

    By default, we apply our own fast and relatively naive equality function to determine whether the arguments provided to your function are equal. You can see the full code here: are-inputs-equal.ts.

    (By default) function arguments are considered equal if:

    1. there is same amount of arguments
    2. each new argument has strict equality (===) with the previous argument
    3. [special case] if two arguments are not === and they are both NaN then the two arguments are treated as equal

    What this looks like in practice:

    import memoizeOne from 'memoize-one';
    
    // add all numbers provided to the function
    const add = (...args = []) =>
      args.reduce((current, value) => {
        return current + value;
      }, 0);
    const memoizedAdd = memoizeOne(add);
    1. there is same amount of arguments
    memoizedAdd(1, 2);
    // the amount of arguments has changed, so underlying add function is called
    memoizedAdd(1, 2, 3);
    1. new arguments have strict equality (===) with the previous argument
    memoizedAdd(1, 2);
    // each argument is `===` to the last argument, so cache is used
    memoizedAdd(1, 2);
    // second argument has changed, so add function is called again
    memoizedAdd(1, 3);
    // the first value is not `===` to the previous first value (1 !== 3)
    // so add function is called again
    memoizedAdd(3, 1);
    1. [special case] if the arguments are not === and they are both NaN then the argument is treated as equal
    memoizedAdd(NaN);
    // Even though NaN !== NaN these arguments are
    // treated as equal as they are both `NaN`
    memoizedAdd(NaN);

    Custom equality function

    You can also pass in a custom function for checking the equality of two sets of arguments

    const memoized = memoizeOne(fn, isEqual);

    An equality function should return true if the arguments are equal. If true is returned then the wrapped function will not be called.

    Tip: A custom equality function needs to compare Arrays. The newArgs array will be a new reference every time so a simple newArgs === lastArgs will always return false.

    Equality functions are not called if the this context of the function has changed (see below).

    Here is an example that uses a lodash.isEqual deep equal equality check

    lodash.isequal correctly handles deep comparing two arrays

    import memoizeOne from 'memoize-one';
    import isDeepEqual from 'lodash.isequal';
    
    const identity = (x) => x;
    
    const shallowMemoized = memoizeOne(identity);
    const deepMemoized = memoizeOne(identity, isDeepEqual);
    
    const result1 = shallowMemoized({ foo: 'bar' });
    const result2 = shallowMemoized({ foo: 'bar' });
    
    result1 === result2; // false - different object reference
    
    const result3 = deepMemoized({ foo: 'bar' });
    const result4 = deepMemoized({ foo: 'bar' });
    
    result3 === result4; // true - arguments are deep equal

    The equality function needs to conform to the EqualityFn type:

    // TFunc is the function being memoized
    type EqualityFn<TFunc extends (...args: any[]) => any> = (
      newArgs: Parameters<TFunc>,
      lastArgs: Parameters<TFunc>,
    ) => boolean;
    
    // You can import this type
    import type { EqualityFn } from 'memoize-one';

    The EqualityFn type allows you to create equality functions that are extremely typesafe. You are welcome to provide your own less type safe equality functions.

    Here are some examples of equality functions which are ordered by most type safe, to least type safe:

    Example equality function types

    // the function we are going to memoize
    function add(first: number, second: number): number {
      return first + second;
    }
    
    // Some options for our equality function
    // ↑ stronger types
    // ↓ weaker types
    
    // ✅ exact parameters of `add`
    {
      const isEqual = function (first: Parameters<typeof add>, second: Parameters<typeof add>) {
        return true;
      };
      expectTypeOf<typeof isEqual>().toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ✅ tuple of the correct types
    {
      const isEqual = function (first: [number, number], second: [number, number]) {
        return true;
      };
      expectTypeOf<typeof isEqual>().toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ❌ tuple of incorrect types
    {
      const isEqual = function (first: [number, string], second: [number, number]) {
        return true;
      };
      expectTypeOf<typeof isEqual>().not.toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ✅ array of the correct types
    {
      const isEqual = function (first: number[], second: number[]) {
        return true;
      };
      expectTypeOf<typeof isEqual>().toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ❌ array of incorrect types
    {
      const isEqual = function (first: string[], second: number[]) {
        return true;
      };
      expectTypeOf<typeof isEqual>().not.toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ✅ tuple of 'unknown'
    {
      const isEqual = function (first: [unknown, unknown], second: [unknown, unknown]) {
        return true;
      };
      expectTypeOf<typeof isEqual>().toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ❌ tuple of 'unknown' of incorrect length
    {
      const isEqual = function (first: [unknown, unknown, unknown], second: [unknown, unknown]) {
        return true;
      };
      expectTypeOf<typeof isEqual>().not.toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ✅ array of 'unknown'
    {
      const isEqual = function (first: unknown[], second: unknown[]) {
        return true;
      };
      expectTypeOf<typeof isEqual>().toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ✅ spread of 'unknown'
    {
      const isEqual = function (...first: unknown[]) {
        return !!first;
      };
      expectTypeOf<typeof isEqual>().toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ✅ tuple of 'any'
    {
      const isEqual = function (first: [any, any], second: [any, any]) {
        return true;
      };
      expectTypeOf<typeof isEqual>().toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ❌ tuple of 'any' or incorrect size
    {
      const isEqual = function (first: [any, any, any], second: [any, any]) {
        return true;
      };
      expectTypeOf<typeof isEqual>().not.toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ✅ array of 'any'
    {
      const isEqual = function (first: any[], second: any[]) {
        return true;
      };
      expectTypeOf<typeof isEqual>().toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ✅ two arguments of type any
    {
      const isEqual = function (first: any, second: any) {
        return true;
      };
      expectTypeOf<typeof isEqual>().toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ✅ a single argument of type any
    {
      const isEqual = function (first: any) {
        return true;
      };
      expectTypeOf<typeof isEqual>().toMatchTypeOf<EqualityFn<typeof add>>();
    }
    
    // ✅ spread of any type
    {
      const isEqual = function (...first: any[]) {
        return true;
      };
      expectTypeOf<typeof isEqual>().toMatchTypeOf<EqualityFn<typeof add>>();
    }

    this

    memoize-one correctly respects this control

    This library takes special care to maintain, and allow control over the the this context for both the original function being memoized as well as the returned memoized function. Both the original function and the memoized function's this context respect all the this controlling techniques:

    • new bindings (new)
    • explicit binding (call, apply, bind);
    • implicit binding (call site: obj.foo());
    • default binding (window or undefined in strict mode);
    • fat arrow binding (binding to lexical this)
    • ignored this (pass null as this to explicit binding)

    Changes to this is considered an argument change

    Changes to the running context (this) of a function can result in the function returning a different value even though its arguments have stayed the same:

    function getA() {
      return this.a;
    }
    
    const temp1 = {
      a: 20,
    };
    const temp2 = {
      a: 30,
    };
    
    getA.call(temp1); // 20
    getA.call(temp2); // 30

    Therefore, in order to prevent against unexpected results, memoize-one takes into account the current execution context (this) of the memoized function. If this is different to the previous invocation then it is considered a change in argument. further discussion.

    Generally this will be of no impact if you are not explicity controlling the this context of functions you want to memoize with explicit binding or implicit binding. memoize-One will detect when you are manipulating this and will then consider the this context as an argument. If this changes, it will re-execute the original function even if the arguments have not changed.

    Clearing the memoization cache

    A .clear() property is added to memoized functions to allow you to clear it's memoization cache.

    This is helpful if you want to:

    • Release memory
    • Allow the underlying function to be called again without having to change arguments
    import memoizeOne from 'memoize-one';
    
    function add(a: number, b: number): number {
      return a + b;
    }
    
    const memoizedAdd = memoizeOne(add);
    
    // first call - not memoized
    const first = memoizedAdd(1, 2);
    
    // second call - cache hit (underlying function not called)
    const second = memoizedAdd(1, 2);
    
    // 👋 clearing memoization cache
    memoizedAdd.clear();
    
    // third call - not memoized (cache was cleared)
    const third = memoizedAdd(1, 2);

    When your result function throws

    There is no caching when your result function throws

    If your result function throws then the memoized function will also throw. The throw will not break the memoized functions existing argument cache. It means the memoized function will pretend like it was never called with arguments that made it throw.

    const canThrow = (name: string) => {
      console.log('called');
      if (name === 'throw') {
        throw new Error(name);
      }
      return { name };
    };
    
    const memoized = memoizeOne(canThrow);
    
    const value1 = memoized('Alex');
    // console.log => 'called'
    const value2 = memoized('Alex');
    // result function not called
    
    console.log(value1 === value2);
    // console.log => true
    
    try {
      memoized('throw');
      // console.log => 'called'
    } catch (e) {
      firstError = e;
    }
    
    try {
      memoized('throw');
      // console.log => 'called'
      // the result function was called again even though it was called twice
      // with the 'throw' string
    } catch (e) {
      secondError = e;
    }
    
    console.log(firstError !== secondError);
    
    const value3 = memoized('Alex');
    // result function not called as the original memoization cache has not been busted
    console.log(value1 === value3);
    // console.log => true

    Function properties

    Functions memoized with memoize-one do not preserve any properties on the function object.

    This behaviour correctly reflected in the TypeScript types

    import memoizeOne from 'memoize-one';
    
    function add(a, b) {
      return a + b;
    }
    add.hello = 'hi';
    
    console.log(typeof add.hello); // string
    
    const memoized = memoizeOne(add);
    
    // hello property on the `add` was not preserved
    console.log(typeof memoized.hello); // undefined

    If you feel strongly that memoize-one should preserve function properties, please raise an issue. This decision was made in order to keep memoize-one as light as possible.

    For now, the .length property of a function is not preserved on the memoized function

    import memoizeOne from 'memoize-one';
    
    function add(a, b) {
      return a + b;
    }
    
    console.log(add.length); // 2
    
    const memoized = memoizeOne(add);
    
    console.log(memoized.length); // 0

    There is no (great) way to correctly set the .length property of the memoized function while also supporting ie11. Once we remove ie11 support then we will set the .length property of the memoized function to match the original function

    → discussion.

    Memoized function type

    The resulting function you get back from memoize-one has almost the same type as the function that you are memoizing

    declare type MemoizedFn<TFunc extends (this: any, ...args: any[]) => any> = {
      clear: () => void;
      (this: ThisParameterType<TFunc>, ...args: Parameters<TFunc>): ReturnType<TFunc>;
    };
    • the same call signature as the function being memoized
    • a .clear() function property added
    • other function object properties on TFunc as not carried over

    You are welcome to use the MemoizedFn generic directly from memoize-one if you like:

    import memoize, { MemoizedFn } from 'memoize-one';
    import isDeepEqual from 'lodash.isequal';
    import { expectTypeOf } from 'expect-type';
    
    // Takes any function: TFunc, and returns a Memoized<TFunc>
    function withDeepEqual<TFunc extends (...args: any[]) => any>(fn: TFunc): MemoizedFn<TFunc> {
      return memoize(fn, isDeepEqual);
    }
    
    function add(first: number, second: number): number {
      return first + second;
    }
    
    const memoized = withDeepEqual(add);
    
    expectTypeOf<typeof memoized>().toEqualTypeOf<MemoizedFn<typeof add>>();

    In this specific example, this type would have been correctly inferred too

    import memoize, { MemoizedFn } from 'memoize-one';
    import isDeepEqual from 'lodash.isequal';
    import { expectTypeOf } from 'expect-type';
    
    // return type of MemoizedFn<TFunc> is inferred
    function withDeepEqual<TFunc extends (...args: any[]) => any>(fn: TFunc) {
      return memoize(fn, isDeepEqual);
    }
    
    function add(first: number, second: number): number {
      return first + second;
    }
    
    const memoized = withDeepEqual(add);
    
    // type test still passes
    expectTypeOf<typeof memoized>().toEqualTypeOf<MemoizedFn<typeof add>>();

    Performance 🚀

    Tiny

    memoize-one is super lightweight at min minified and minzip gzipped. (1KB = 1,024 Bytes)

    Extremely fast

    memoize-one performs better or on par with than other popular memoization libraries for the purpose of remembering the latest invocation.

    The comparisons are not exhaustive and are primarily to show that memoize-one accomplishes remembering the latest invocation really fast. There is variability between runs. The benchmarks do not take into account the differences in feature sets, library sizes, parse time, and so on.

    Expand for results

    node version 16.11.1

    You can run this test in the repo by:

    1. Add "type": "module" to the package.json (why is things so hard)
    2. Run yarn perf:library-comparison

    no arguments

    Position Library Operations per second
    1 memoize-one 80,112,981
    2 moize 72,885,631
    3 memoizee 35,550,009
    4 mem (JSON.stringify strategy) 4,610,532
    5 lodash.memoize (JSON.stringify key resolver) 3,708,945
    6 no memoization 505
    7 fast-memoize 504

    single primitive argument

    Position Library Operations per second
    1 fast-memoize 45,482,711
    2 moize 34,810,659
    3 memoize-one 29,030,828
    4 memoizee 23,467,065
    5 mem (JSON.stringify strategy) 3,985,223
    6 lodash.memoize (JSON.stringify key resolver) 3,369,297
    7 no memoization 507

    single complex argument

    Position Library Operations per second
    1 moize 27,660,856
    2 memoize-one 22,407,916
    3 memoizee 19,546,835
    4 mem (JSON.stringify strategy) 2,068,038
    5 lodash.memoize (JSON.stringify key resolver) 1,911,335
    6 fast-memoize 1,633,855
    7 no memoization 504

    multiple primitive arguments

    Position Library Operations per second
    1 moize 22,366,497
    2 memoize-one 17,241,995
    3 memoizee 9,789,442
    4 mem (JSON.stringify strategy) 3,065,328
    5 lodash.memoize (JSON.stringify key resolver) 2,663,599
    6 fast-memoize 1,219,548
    7 no memoization 504

    multiple complex arguments

    Position Library Operations per second
    1 moize 21,788,081
    2 memoize-one 17,321,248
    3 memoizee 9,595,420
    4 lodash.memoize (JSON.stringify key resolver) 873,283
    5 mem (JSON.stringify strategy) 850,779
    6 fast-memoize 687,863
    7 no memoization 504

    multiple complex arguments (spreading arguments)

    Position Library Operations per second
    1 moize 21,701,537
    2 memoizee 19,463,942
    3 memoize-one 17,027,544
    4 lodash.memoize (JSON.stringify key resolver) 887,816
    5 mem (JSON.stringify strategy) 849,244
    6 fast-memoize 691,512
    7 no memoization 504

    Code health 👍

    • Tested with all built in JavaScript types
    • Written in Typescript
    • Correct typing for Typescript and flow type systems
    • No dependencies

    Install

    npm i memoize-one

    DownloadsWeekly Downloads

    7,026,617

    Version

    6.0.0

    License

    MIT

    Unpacked Size

    35.6 kB

    Total Files

    13

    Last publish

    Collaborators

    • alexreardon