Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the async and race conditions pattern
A missing await, results in the wrong order, and updates that overwrite each other under load.
What went wrong: return value * 2 is inside the timer callback. doubleLater itself ends straight away and returns undefined.
The fix: return new Promise((resolve) => setTimeout(() => resolve(value * 2), 1));
Remember: you cannot return a later value from a callback. Return a promise instead.
The pattern behind it: async and race conditions.
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