cache.js

let cache = {}

const complex_computation = (a, b, timeout=5000, callback) => {
  setTimeout(() => {
    callback(null, a + b)
  }, timeout)
}

const cached_computation = (a, b, callback) => {
  const key = a + ':' + b

  if (cache[key]) {
    return callback(null, cache[key])
  }

  complex_computation(a, b, 10000, (err, data) => {
    cache[key] = data
    callback(err, data)
  })
}

// EXEC
console.time("QueryTime")
cached_computation(2, 3, (err, data) => {
  if (err != null) {
    console.log(error)
    return console.timeEnd("QueryTime")
  }
  
  console.log(data)
  console.timeEnd("QueryTime")
})