UnhandledPromiseRejectionWarning in Node.js — What It Means and How to Fix It

This means a Promise was rejected and no .catch() or try/catch handled it. In modern Node it crashes the process.

What it means and why it happens

Typical causes: missing await in try/catch, forgetting .catch(), or errors in async event handlers.

Read the full message: it names the file and line where the problem was detected, which is the best place to start.

What you see

Practical examples

Code that triggers it

async function run() { throw new Error('boom') }
run()

The fix

run().catch(err => { console.error(err); process.exitCode = 1 })

Global safety net

process.on('unhandledRejection', (err) => { console.error(err); process.exit(1) })

Common mistakes

• Calling async functions without awaiting or catching.
• try/catch around code that is not awaited.
• Ignoring rejections in forEach callbacks.

Key takeaways

• UnhandledPromiseRejectionWarning: This means a Promise was rejected and no .catch() or try/catch handled it.
• Read the message and the line number first.
• Fix the cause, don't just silence the error.

FAQ

Does Node still just warn?

Since Node 15 unhandled rejections crash the process by default.

How do I find which line caused UnhandledPromiseRejectionWarning?

The error message and stack trace show the file and line; start there and work backwards.