memoize-lit

A memoization library that stores the results of expensive function calls and returns the cached result when the same inputs occur again.

Note: This helper works both with synchronous and asynchronous functions, e.g. Promises.

This library is a cherry-picked mixture of several popular memoisation libraries to make memoisation both easy and straight forward.

Requirements

• Node v10+
• npm v6+

Install

# Using npm
$ npm install memoize-lit

# Using yarn
$ yarn add memoize-lit

Examples

Synchronous

import { memoize } from 'memoize-lit';

const multiply = (a, b) => a * b;
const memoizedMultiply = memoize(multiply);

memoizedMultiply(2, 3); // 6

memoizedMultiply(2, 3); // 6
// Multiply function is not executed and previous result is returned

memoizedMultiply(1, 3); // 3
// Multiply function is called as arguments have changed

memoizedMultiply(1, 3); // 3
// Multiply function is not executed and previous result is returned

memoizedMultiply(2, 3); // 6
// Multiply function is called as arguments have changed.

Asynchronous

import { memoize } from 'memoize-lit';
import axios from 'axios';

const memoizedAxios = memoize(axios, { maxAge: 100 });

(async () => {
  await memoizedAxios('https://joelvoss.com');

  await memoizedAxios('https://joelvoss.com');
  // Axios is not executed and previous result is returned

  setTimeout(() => {
    await memoizedAxios('https://joelvoss.com');
    // Axios function is called as `maxAge` has expired
  }, 200);
})();

API

memoize(fn, options?)

Create a memoized version of fn. You can provide a custom configuration as the second argument.

fn

Input function to memoize.

import { memoize } from 'memoize-lit';

// (1) Memoize the `multiply` function
const multiply = (a, b) => a * b;
const memoizedMultiply = memoize(multiply);

// (2) Use it normally
memoizedMultiply(2, 3); // 6

options

Provide a custom equality function and/or the maxAge time in milliseconds.

// Signature

type EqualityFn = (newArgs: any[], lastArgs: any[]) => boolean;

type Options = {
  isEqual?: EqualityFn;
  maxAge?: number;
};

import { memoize } from 'memoize-lit';
import axios from 'axios';

// (1) Memoize axios
const memoizedAxios = memoize(axios, { maxAge: 100 });

(async () => {
  // (2) Use it normally
  await memoizedAxios('https://joelvoss.com');
})();

The default equality function is a shallow equal check of all arguments (each argument is compared with ===). If the length of arguments change, then the default equality function makes no shallow equality checks.

The default maxAge value in milliseconds is 2147483647, which is the biggest signed 32-bit integer value possible.

When your function throws or the promise rejects

In essence: There is no caching if your function throws or is rejected.

If your result function throws then the memoized function will also throw. This will not drop the memoized result. This means that the memoized function will pretend like it was never called with arguments that made it throw.

This behaviour is different for Promises, because a Promise can never throw but instead return a rejected state. If a Promise is being rejected, it is being marked as stale so the next invocation returns a fresh result.

Note: A rejected promise never overwrites an intermediate successful promise. In this case the rejected promise is simply ignored.

This library does not handle promise rejections for you, so always make sure to wrap an async memoized function in a try / catch block.

Development

[1] Install dependencies

# Using npm
$ npm install

# Using yarn
$ yarn

[2] Validate setup

$ ./Taskfile.sh validate

[3] Start development by running tests in watch-mode

$ ./Taskfile.sh test -w

This project was bootstrapped with @jvdx/core.