ScriptdrillRun only once
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
Return a function that calls `fn` the first time it is called, with that call's arguments, and returns `fn`'s result. Every later call returns that same first result without calling `fn` again, even when the result was `undefined` or `0`.
What this exercise teaches
A separate done flag records that fn already ran. Testing the stored result instead fails as soon as fn returns undefined, 0 or another falsy value.
A hint if you get stuck
Keep two variables outside the returned function: a `done` flag and the `result`. Test the flag, not the result.
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