Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the scope and closure bugs pattern
Every callback reports the last value, a counter never increments, UnboundLocalError on a variable you can see.
What went wrong: result is created with let inside the if block. It only exists inside that block, so the return line cannot see it.
The fix: declare let result = null; before the loop, then assign result = nums[i]; inside the if. Add break to stop at the first one.
Remember: let and const only live inside the { } where you write them.
The pattern behind it: scope and closure bugs.
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