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fp-light-memoize

npm i @sullux/fp-light-memoize source test

Memoization is the caching of results for a given set of arguments. Memoization is useful for pure functions that have a high computational cost or asynchronous latency.

• memoize
• defaultMemoizeArgsEqual

memoize

memoize<T>( fn: (...args: Array<any>) => T, equal: ?(leftArgs: Array<any>, rightArgs: Array<any>) => boolean ): T

• fn: the function to memoize.
• equal: (default defaultMemoizeArgsEqual) the function to test equality of arguments.

When the memoized function is called, it checks to see if the given arguments have already been cached. It checks by calling equal for each set of cached arguments. If it finds a match, it returns the corresponding cached result; otherwise, it executes fn and caches and returns the result.

The built-in Node.js require function is a good example of a memoized function: it will load the required file the first time (incurring asynchronous latency) and will return the originally loaded value on every subsequent call. A naive implementation of an asynchronous require might look like this:

const { readFile } = require('fs')
const { promisify } = require('util')
const { createContext, runInContext } = require('vm')
const { pipe } = require('@sullux/fp-light-pipe')
const { memoize } = require('@sullux/fp-light-memoize')

const readFileAsync = promisify(readFile)
  .then(data => data.toString())

const createVm = js => {
  const sandbox = {
    ...globals,
    module: { exports: {} },
  }
  const context = createContext(sandbox)
  runInContext(js, context)
  return sandbox.module.exports
}

const requireAsync = memoize(pipe(
  readFileAsync,
  createVm
))

module.exports = { requireAsync }

defaultMemoizeArgsEqual

defaultMemoizeArgsEqual(leftArgs: Array<any>, rightArgs: Array<any>): boolean

This is the default equality test for memoize. This is a shallow test that compares the argument count and shallow equality of each argument using Oject.is. A custom implementation might choose deep equality to enable interface equality over reference equality, for example.