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When Fixing a Broken Script Accidentally Creates a Second, Conflicting Handler

Field Note #164
🔬 Resolved 🔴 Advanced ⏱ 30 Minutes ✓ Observation from Experience

⚡ Quick Fix (TL;DR)

The Fix: 1. Identify every place a given element's behavior might be bound, not just the one that's obviously broken.
2. Before patching a broken handler, check whether a working handler already exists elsewhere for the same element.
3. If two handlers do the same logical thing (like "toggle open, close others"), fixing the broken one without removing the redundant one will not restore correct behavior — it will create a race between two handlers that cancels the intended effect.

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The symptom
A page’s FAQ accordion appeared to work — items opened when clicked — but this was on a page where a *different*, broken embedded script (see: base64 script syntax errors) was also present, targeting the same FAQ elements.

Initial assumption
The first instinct was to fix the broken script the same way as on other pages: correct the syntax error and move on.

That assumption would have introduced a new, worse bug.

Investigation

This particular page had FAQ items with an inline `onclick` attribute directly in the HTML, handling the open/close toggle. Separately, the same broken base64 script *also* contained logic meant to bind a click listener to those same FAQ items — but that logic was currently inert because the surrounding script failed to parse.
 
If the script’s syntax error were fixed in isolation, both handlers would become active: the inline `onclick` and the script’s own `addEventListener`. Since click events on a child element bubble up to a parent, both handlers would fire on a single click. Tracing the logic: the first handler would open the item, then the second handler — seeing it now open — would immediately close it again. Net visible effect: clicking an item would appear to do nothing.

What to check
When a page has more than one mechanism that could be responsible for the same interactive behavior (an inline `onclick` attribute *and* a script-based `addEventListener`, for example):
 
1. Identify every place a given element’s behavior might be bound, not just the one that’s obviously broken.
2. Before patching a broken handler, check whether a working handler already exists elsewhere for the same element.
3. If two handlers do the same logical thing (like “toggle open, close others”), fixing the broken one without removing the redundant one will not restore correct behavior — it will create a race between two handlers that cancels the intended effect.

Current finding
The correct fix was not just repairing the script’s syntax — it was removing the inline `onclick` attributes entirely and relying on a single, corrected script-based handler, so there was only one source of truth for the toggle behavior.

Troubleshooting lesson
A broken script and a working inline handler can coexist quietly, because the broken script never activates. Fixing the script’s syntax without checking for this overlap can turn a single silent failure into a new, harder-to-diagnose bug where the feature “does nothing” instead of failing outright. Always check for duplicate handlers before assuming a syntax fix is sufficient.

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