nextjs - 💡(How to fix) Fix `next dev`: Instrumentation hook is still analyzed for the edge runtime despite never running in the edge runtime [5 comments, 4 participants]

1. See the error in your console: Ecmascript file had an error 4 | console.error("Unhandled rejection:", reason); 5 | console.error("Promise:", promise); Current: There is an error logged from analysis of the instrumentation hook for edge runtimes, despite the instrumentation hook never running in the edge runtime. This error doesn't actually break anything at runtime it seems. Expected: No error should appear. With the new proxy.ts enabling a full nodejs runtime version of Next.js, the instrumentation hook never runs its "edge" version (verified via the console log in the minimal repro, the register hook only runs with process.env.NEXT_RUNTIME set to "nodejs"). Despite this, it seems like there is still some checking for nodejs-only APIs running for the instrumentation hook, which produce console warnings.

TL;DR

The issue can be fixed by modifying the instrumentation hook to check for the NEXT_RUNTIME environment variable before accessing Node.js-only APIs.

Guidance

• Verify that the instrumentation hook is only running in the correct runtime environment by checking the value of process.env.NEXT_RUNTIME.
• Modify the instrumentation hook to conditionally access Node.js-only APIs based on the value of process.env.NEXT_RUNTIME.
• Investigate why the warnings only appear after visiting a page and not during the initial instrumentation hook run.
• Consider adding a check for the process global being available before accessing it to prevent warnings.

Example

export const register = async () => {
  console.log("registering instrumentation", process.env.NEXT_RUNTIME);
  if (process.env.NEXT_RUNTIME === 'nodejs') {
    process.on("unhandledRejection", (reason, promise) => {
      console.error("Unhandled rejection:", reason);
      console.error("Promise:", promise);
    });
  }
};

Notes

The provided example is a minimal code snippet and may need to be adapted to the actual instrumentation hook code. The issue seems to be related to the instrumentation hook accessing Node.js-only APIs in the wrong runtime environment.

Recommendation

Apply workaround: Modify the instrumentation hook to conditionally access Node.js-only APIs based on the value of process.env.NEXT_RUNTIME, as shown in the example. This should prevent the warnings from appearing in the incorrect runtime environment.