Cloudflare Workers offer a powerful platform to run JavaScript at the edge. However, when a Cloudflare Worker throws an unhandled exception, you might see the following error:
Error 1101: Worker threw exception
This error indicates that during the processing of a request, the Worker’s JavaScript code encountered a runtime error, causing it to fail before returning a proper response. In this article, we’ll explore what causes Error 1101, review common pitfalls, and provide a step-by-step troubleshooting guide with actionable solutions.
What Does Error 1101 Mean?
When you see Error 1101, it means your Worker script has encountered an error it could not handle. This is often due to issues in your code such as syntax mistakes, unresolved promises, or mismanagement of context. Rather than failing silently, Cloudflare displays this error to help you identify that there’s an issue with your Worker’s execution.
Common Causes and Their Solutions
Below is a table of typical causes for Cloudflare Error 1101 and recommended actions to address them:
| Common Cause | Description | Recommended Action |
|---|---|---|
| Syntax or Runtime Errors | Bugs, typos, or incorrect API usage in your JavaScript code. | Review your code carefully, use linters, and run tests locally. |
| Unresolved Promises | Promises that never resolve or reject, causing the Worker to hang indefinitely. | Ensure every promise is handled appropriately (resolve/reject) with proper timeouts. |
| Improper Context Usage | Destructuring context methods (e.g., waitUntil) without preserving the correct this binding. | Avoid destructuring methods or use .bind()/.apply() to maintain the correct context. |
| WebSocket or I/O Issues | Unclosed WebSocket connections or improper handling of I/O objects. | Implement proper cleanup (e.g., close WebSocket connections) and error handling. |
| Exceeding Resource Limits | Excessive CPU time or memory usage may indirectly trigger errors. | Optimize your code to stay within Cloudflare’s limits, and perform heavy tasks externally if needed. |
Other Cloudflare Worker Error Codes
Cloudflare uses a range of error codes for different issues. Here’s a brief overview, including Error 1101:
| Error Code | Meaning |
|---|---|
| 1101 | Worker threw a JavaScript exception. |
| 1102 | Worker exceeded CPU time limit. |
| 1103 | The owner of this worker needs to contact Cloudflare Support. |
| 1015 | Worker hit the burst rate limit. |
| 1019 | Worker hit loop limit. |
| 1021 | Worker requested a host it cannot access. |
| 1022 | Cloudflare failed to route the request to the Worker. |
| 1024 | Worker cannot make a subrequest to a Cloudflare-owned IP address. |
| 1027 | Worker exceeded free tier daily request limit. |
| 1042 | Worker tried to fetch from another Worker on the same zone. |
While Error 1101 specifically pertains to a thrown exception, understanding other error codes can be useful for comprehensive troubleshooting.
Step-by-Step Troubleshooting Guide
Follow these steps to diagnose and resolve Cloudflare Error 1101:
| Steps | Action | Details |
|---|---|---|
| 1 | Review Worker Metrics and Logs | – Log in to your Cloudflare dashboard. – Check the Workers Metrics section for patterns or spikes in errors. |
| 2 | Use Wrangler Tail for Real-Time Logs | – Run wrangler tail from your terminal to stream real-time logs from your Worker. – Look for the exceptions field in the JSON output to pinpoint the error. |
| 3 | Debug Your Code Locally | – Reproduce the issue in a local environment. – Check for unresolved promises and syntax errors. – Use debuggers or linters to inspect your code. |
| 4 | Fix Identified Issues | – Address any syntax, logic, or context issues identified during debugging. – For unresolved promises, ensure every asynchronous call resolves or rejects. |
| 5 | Implement Fallbacks and Logging | – Consider using event.passThroughOnException() to route requests to your origin in case of errors. – Integrate a logging service (e.g., Sentry) for more insight. |
| 6 | Redeploy and Monitor | – Redeploy your Worker with the fixes. – Monitor logs using wrangler tail and the dashboard to ensure the error is resolved. |
Best Practices for Preventing Future Errors
Always Handle Promises:
- Make sure every promise in your code is either resolved or rejected. Unhandled promises can lead to hanging requests or runtime exceptions.
Maintain Proper Context:
- When using methods from the context (like
waitUntil), avoid destructuring unless you rebind the method to its original context.
Log Detailed Information:
- Set up external logging to capture detailed error reports. This can help in identifying issues that may not be immediately visible in the dashboard.
Use Fallback Mechanisms:
- Implement strategies like
event.passThroughOnException()so that if your Worker fails, your origin server can serve the request instead of the end-user seeing an error page.
Conclusion
Error 1101 is a clear sign that your Cloudflare Worker has encountered an unhandled exception. By methodically reviewing your Worker’s logs, debugging your code locally, and following the troubleshooting steps provided above, you can identify and fix the underlying issue.
