Javascript Memoization Implementation

Question

I've been debating this topic with my mates at work. I would like to know from you guys, if this is, actually, the right way of implementing the memoization.

function memoize(result) {
  let cache = {};

  return function() {
    if (cache[result]) {
      // returns cached result / no calculation
      return cache[result];
    }
    // calculating...
    cache[result] = result;
    return cache[result];
  };
}

function expensiveCalculation() {
  let counter = 0;
  for (let i = 0; i < 1000000; i++) {
    counter += i;
  }
  return counter;
}

console.time("FirstCalculation");
const memoizedExpensiveCalculation = memoize(expensiveCalculation());
console.timeEnd("FirstCalculation");

console.time("1_Memoized");
memoizedExpensiveCalculation();
console.timeEnd("1_Memoized");

console.time("2_Memoized");
memoizedExpensiveCalculation();
console.timeEnd("2_Memoized");

console.time("3_Memoized");
memoizedExpensiveCalculation();
console.timeEnd("3_Memoized");

The time logs reveals, in fact, the first time takes much more time (which we would expect) and less time afterwards.

Your code makes no sense your result is the key and what you return? — epascarello, Jan 25 '22 at 17:26
Does this answer your question? [How to create a memoize function](https://stackoverflow.com/questions/30386943/how-to-create-a-memoize-function) — apple apple, Jan 25 '22 at 17:28

apple apple · Answer 1 · 2022-01-25T17:24:51.587

0

it's not correct

The code you shows

function memoize(result) {
  let cache = {};

  return function() {
    if (cache[result]) {
      // returns cached result / no calculation
      return cache[result];
    }
    // calculating...
    cache[result] = result;
    return cache[result];
  };
}

is basically

function memoize(result) {
  return result
}

in memoization what you cache is input/output pair and skip real function call when input match.

edited Jan 25 '22 at 17:24

answered Jan 25 '22 at 17:22

apple apple

10,292
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What should be changed? – JGS Jan 25 '22 at 17:24
@JGS well it's completely wrong. You need to rewrite whole thing. I've update the answer a little. – apple apple Jan 25 '22 at 17:25
Could you give me a code snippet as an example? – JGS Jan 25 '22 at 17:27
@JGS https://stackoverflow.com/questions/30386943/how-to-create-a-memoize-function is an example. – apple apple Jan 25 '22 at 17:28
I was expecting that you could fill in the missing parts but rather you told me "rewrite the whole thing". That was quite brutal and toxic :P But thanks anyway! – JGS Jan 25 '22 at 18:29

score 0 · Accepted Answer · answered Jan 25 '22 at 17:32

0

something like:

function get(func) {
  let cache = {};

  return function(key) {
    if (key in cache) {
      return cache[key];
    }
    cache[key] = func(key);
    return cache[key];
 };
}

function expensiveCalculation(param) {
  console.log('expensive calculation runs')
  let counter = 0;
  for (let i = 0; i < 10000; i++) {
    counter += i;
  }
  return param*2;
}
const memo = get(expensiveCalculation)
console.log('start')
console.log('first try');
console.log(memo(10));
console.log('second try');
console.log(memo(10));

answered Jan 25 '22 at 17:32

Nir O.

1,563
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This is actually very useful. You grabbed my implementation and filled in what's missing. Thank you! – JGS Jan 25 '22 at 18:27
with pleasure ! will be glad if you accept this answer :) – Nir O. Jan 25 '22 at 18:38

Javascript Memoization Implementation

2 Answers2