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typescript.promise_no_catch

Stability High Causes Production Outages

Detects Promises without .catch() handler or try/catch in async functions.

Why It Matters

Unhandled promise rejections can crash Node.js:

Process crash — Node.js 15+ crashes on unhandled rejections
Silent failures — Earlier versions just warn and continue
Lost errors — Rejections vanish into the void
Unpredictable state — Operations fail but code assumes success

Every promise must have error handling.

Example

// ❌ Before
fetchData().then(data => process(data));
// If fetchData rejects, nothing catches it

async function loadUser() {
    const user = await getUser(id);  // No try/catch
    return user;
}

// ✅ After
fetchData()
    .then(data => process(data))
    .catch(error => console.error('Failed to fetch:', error));

async function loadUser() {
    try {
        const user = await getUser(id);
        return user;
    } catch (error) {
        console.error('Failed to load user:', error);
        throw error;
    }
}

What Unfault Detects

.then() without .catch()
await without surrounding try/catch
Floating promises (not awaited or returned)

Auto-Fix

Unfault can add .catch() handlers or wrap in try/catch when the promise chain is clearly identified.

Best Practices

// Always chain .catch() with .then()
promise
    .then(handleSuccess)
    .catch(handleError);

// Use try/catch with async/await
async function doWork() {
    try {
        await step1();
        await step2();
    } catch (error) {
        handleError(error);
    }
}

// For fire-and-forget, handle explicitly
void sendAnalytics(event).catch(console.error);

// Top-level async
main().catch(error => {
    console.error('Unhandled error:', error);
    process.exit(1);
});

Node.js Behavior

// Node.js 15+ crashes on unhandled rejections
// You can customize this:
process.on('unhandledRejection', (reason, promise) => {
    console.error('Unhandled Rejection:', reason);
    // Decide: log and continue or exit
});