Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the logic errors pattern
The wrong operator, an inverted condition, a formula the right way round but backwards.
What went wrong: The logical OR operator (||) treats 0 as falsy and falls back to the default 15% discount.
The fix: Use the nullish coalescing operator (??) so only null or undefined triggers the default: promoPercent ?? 15
Remember: In JavaScript, 0 is falsy with ||, but preserved with ??.
The pattern behind it: logic errors.
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<iframe src="https://trybughunt.com/embed/6d545023-3e56-4a64-afe8-3108eb116179" title="Debugging challenge: Zero percent promo code triggers fallback discount" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe>
<p style="font-size:14px">Debugging challenge from <a href="https://trybughunt.com/challenges/6d545023-3e56-4a64-afe8-3108eb116179">TryBugHunt</a></p>