Скачать или смотреть Resolving TypeError in NestJS and MQTT Using PM2/NodeJS

Encounter a `TypeError` when running your NestJS and MQTT application with PM2/NodeJS? Discover how to fix the issue by avoiding the use of environment variables in `@ MessagePattern`.
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Debugging NestJS with MQTT: A TypeError Encountered

When developing applications using NestJS in combination with MQTT, users sometimes run into errors particularly when trying to deploy with PM2 or running directly with Node.js. This guide dives into a specific issue that one developer faced: encountering a TypeError related to message patterns and how it was resolved.

The Problem Statement

While setting up a NestJS application to handle MQTT messages via MessagePatterns, the developer encountered an issue when attempting to run the compiled project Node.js. Specifically, after deploying using the following command:

[[See Video to Reveal this Text or Code Snippet]]

An error was thrown indicating an inability to read properties from an object, especially involving the MQTT resubscribe:

[[See Video to Reveal this Text or Code Snippet]]

This surfaced during the subscription process integrated into the application's main service.

Symptoms Observed

The developer noted the following key observations:

The application worked flawlessly when run with the command yarn nx serve api.

Building the project using yarn nx run-many --t=build --configuration=production was successful.

The issue arose only when executing the main script directly via Node.js.

Attempts to Resolve the Error

In an effort to fix the error, several troubleshooting steps were taken:

Testing different versions of Node.js.

Trying various versions of the MQTT library.

Commenting out sections of code to isolate the cause of the issue.

Despite all efforts, the issue persisted.

The Solution: Environment Variables in MessagePatterns

After exhaustive debugging, the solution was identified. The problem primarily arose from the way environment variables were used within the @ MessagePattern decorator. The initial implementation used environment variables as follows:

[[See Video to Reveal this Text or Code Snippet]]

This approach worked without issues when running directly from NX/NestJS but caused complications when running the compiled code with Node.js.

Fixing the Issue

To resolve the error, it was recommended to use hardcoded strings for the @ MessagePattern, as such:

[[See Video to Reveal this Text or Code Snippet]]

This change appeared to eliminate the TypeError, allowing the application to run smoothly both in development and production environments.

Conclusion

Running applications developed with NestJS and MQTT can be challenging at times, particularly with deployment strategies. As demonstrated, common issues like TypeError can stem from seemingly harmless coding practices, such as using environment variables directly in important areas of the code.

By simply changing the implementation of the @ MessagePattern from using environment variables to hardcoded strings, not only was the error resolved, but the application's performance remained intact throughout.

If you face similar challenges in your application, remember to examine how you are integrating environment variables and consider simplifying your patterns where possible.

Feel free to reach out if you have any further queries or require assistance with your NestJS applications. Happy coding!