Memoization example

memoize.js

function memoize(func) {
  const map = new Map()
  return function() {
    const args = Array.prototype.slice.call(arguments)
    const key = JSON.stringify(args)
    if (! map.has(key)) map.set(key, func.apply(null, args))
    return map.get(key)
  }
}

// example to use

function add(a,b) {  
  function delayed() { return a + b }
  for(let i=1e8; i > 0; i--) { delayed() }
  return delayed()
}

const _add = memoize(add)

console.log(_add(3,4))
console.log(_add(3,5))
console.log(_add(3,4))
console.log(_add(3,5))