# JavaScript Silent Crash: Block-Scoped `const` in `try`

**Pattern:** A `const` (or `let`) declared inside a `try {}` block is referenced
outside the block. JavaScript throws a `ReferenceError` that silently crashes
async event handlers — no error visible in the UI, no console output if the
handler is an `addEventListener` callback calling an `async function`.

## Example

```javascript
async function handleFinancialCompletion() {
    // ...
    try {
        const roData = getROData(roId);  // block-scoped to try
        // ...
    } catch (e) {}

    // BUG: roData is undefined here — ReferenceError
    if (roData) {
        roData.statusHistory.push({ ... });
    }
    // ...
}
```

## Why it's silent

The `completeBtn.addEventListener('click', (e) => { handleFinancialCompletion(); })`
does NOT catch the rejected promise from the async function. The ReferenceError
propagates as an unhandled promise rejection — which browsers log but the UI
shows nothing. The user sees "nothing happens."

## Fix

Declare the variable OUTSIDE the `try` block:

```javascript
const roData = getROData(roId);  // outside try
try {
    const servicesLines = roData?.services ? ...;
    // ...
} catch (e) {}
// roData is accessible here
if (roData) { ... }
```

## Detection

Grep for `const.*=.*try` patterns or any variable accessed after a `} catch`
that was declared inside the `try`:
```bash
grep -n 'const ' file.js | while read line; do
    # Check if any const declared in try block is used after catch
    ...
done
```