caching.js

const add = (a, b) => (a + b);

const cachingFunc = (cacheObj = {}) => {
  const cache = cacheObj;

  return (a, b) => {
    let hash = `${a}:${b}`;
    if (!cache[hash]) {
      console.log('Computing result');
      cache[hash] = add(a, b);
    } else {
      console.log('Skipping computation');
    }
    return cache[hash];
  }
}

console.log('Test without pre-existing cache');
const cachingAdd = cachingFunc();
cachingAdd(3, 4);
cachingAdd(3, 5);
cachingAdd(3, 4);

const cachingAddv2 = cachingFunc({
  '3:7': 10,
  '4:2': 6
});

console.log('Test with existing cache');
cachingAddv2(3, 7);