Test demostrating basic memoization for a cached parameter, using previously calculated result

memoization.js

// our cache
let cache = {
  val: null,
  res: null
}

const myLongTask = num => {
  // if parameter is equal to our cached value, we don't repeat the calculation
  if (num === cache.val) { 
    const t1 = new Date().valueOf()
    const t2 = new Date().valueOf()
    console.log(`Parameter was memoized. Operation time(ms): ${t2-t1}`)
    return cache.res
  }

  // since parameter was not equal to our cached value, it needs to do the calculations
  const t1 = new Date().valueOf()
  const res = stress(num) // mock some performance hit
  cache = {val: num, res: res} // store parameter and response in our cache
  const t2 = new Date().valueOf()
  console.log(`Parameter not memoized. Operation time(ms): ${t2-t1}`)
  return res
}

// intensive operation
const stress = (num)  => {
  let newNum = 0
  while (newNum < 2000000000) {
    newNum += num
  }
  return newNum
}

// use a combination of different and same parameters
const myArray = [1,2,3,4,4,4,4,4,4,4,4,4,4,5]

// if passing same parameter than one cached = memoized value (instant)
// if passing diff parameter than one cached = recalculation (slow)
myArray.forEach(number => {
  myLongTask(number)
})