14. Implement a general memoization function - `memo()`

Memoization is a common technique to boost performance. If you use React, you definitely have used React.memo before.

Memoization is also commonly used in algorithm problem, when you have a recursion solution, in most cases, you can improve it by memoization, and then you might be able to get a Dynamic Programming approach.

So could you implement a general memo() function, which caches the result once called, so when same arguments are passed in, the result will be returned right away.

const func = (arg1, arg2) => {
  return arg1 + arg2
}

const memoed = memo(func)

memoed(1, 2) 
// 3, func is called

memoed(1, 2) 
// 3 is returned right away without calling func

memoed(1, 3)
// 4, new arguments, so func is called

The arguments are arbitrary, so memo should accept an extra resolver parameter, which is used to generate the cache key, like what _.memoize() does.

const memoed = memo(func, () => 'samekey')

memoed(1, 2) 
// 3, func is called, 3 is cached with key 'samekey'

memoed(1, 2) 
// 3, since key is the same, 3 is returned without calling func

memoed(1, 3) 
// 3, since key is the same, 3 is returned without calling func

Default cache key could be just Array.from(arguments).join('_')

note

It is a trade-off of space for time, so if you use this in an interview, please do analyze how much space it might cost.