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: each const discounted only exists inside its own { } block. The return line is outside both, so it cannot see either one.
The fix: let discounted; before the if, then discounted = price * 0.9; and discounted = price; in the branches.
Remember: declare a variable in the block where you use it.
The pattern behind it: scope and closure bugs.
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