ScriptdrillMemoize
A JavaScript exercise from Scriptdrill. Solve it with a code editor in your browser that runs your function against example and hidden tests, and it is checked the moment you submit.
The task
`fn` takes one argument. Return a function that computes `fn(x)` only the first time it sees `x` and returns the stored result after that. Arguments are told apart the way a `Map` tells keys apart, so `1` and `"1"` are different. Results such as `0`, `false` and `undefined` are cached too. Each memoized function has its own cache.
What this exercise teaches
A Map keeps keys with their type, which a plain object would turn into strings. Asking has() rather than testing the cached value keeps falsy results cached, and creating the Map inside memoize gives every memoized function its own cache.
A hint if you get stuck
Create a `new Map()` inside `memoize`. In the returned function, use `cache.has(x)` (not the stored value) to decide whether to call `fn`.
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