Express 5.1 source map issue not present in 4.21

[arenddeboer]

Today I ran into an issue where express 5.1 somehow prevents source maps / line numbers from working.
Throwing an error inside a route handler results in a useless call stack referring to line 1 column 9827928
I was unable to create an isolated test case, the problematic code worked well in my small test project.

I still wanted to at least start a discussion in case someone else runs into this.
I do have a somewhat unconventional way to run my code which may or may not have anything to do with this issue:
node --experimental-transform-types --enable-source-maps --import tsx server.ts
Anyway, downgrading express to 4.x solved the issue.

But if others also run into this, maybe it's worth investigating further.

[bjohansebas]

What would really help is if you could provide an example of some code and the steps to follow to debug it. It seems more like a Node.js bug than an Express bug, but to be able to say that, it would be great if you could share a code example.

[arenddeboer]

For sure. I did have a small reproduction test project but it did not show the issue as in my main project.
But you are right sharing some code is still important.
I did find some locked issues with similar problems, so maybe there is a common denominator.

Here is the code, it seems the moment I awaited a promise inside the route handler, the source map reference got lost:

// express 5.1
async function throwError(req: Request, res: Response, next: NextFunction) {
  await Promise.resolve()
  console.error('Do we have a .ts file line number?')
  throw new Error('Do we have a .ts file line number?')
}
expressServer.use(async (req, res, next) => {
  await throwError(req, res, next)
  next()
})

// Error
Do we have a .ts file line number?
Error: Do we have a .ts file line number?
    at throwError (file:///<absolute-path>/server/serverPA3.ts:1:3557)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
    at async file:///<absolute-path>/server/serverPA3.ts:1:3676
    


// Without await in route handler works:
async function throwError(req: Request, res: Response, next: NextFunction) {
  await Promise.resolve()
  console.error('Do we have a .ts file line number?')
  throw new Error('Do we have a .ts file line number?')
}
expressServer.use(async (req, res, next) => {
  throwError(req, res, next)
  next()
})

// Error
Do we have a .ts file line number?
Error: Do we have a .ts file line number?
    at throwError (server/serverPA3.ts:191:8)
 ⨯ unhandledRejection:  Error: Do we have a .ts file line number?
    at throwError (server/serverPA3.ts:191:8)



// Just throwing an error inside the route handlers also doesn't work
expressServer.use(async (req, res, next) => {
  console.error('Do we have a .ts file line number?')
  throw new Error('Do we have a .ts file line number?')
  next()
})

// Error
Do we have a .ts file line number?
Error: Do we have a .ts file line number?
    at file:///<absolute-path>/server/serverPA3.ts:1:3733

As a note, in the working non awaited version, the error has a relative path, the minified version throws an absolute path reference.

Thanks for looking into it.

[bjohansebas]

Tomorrow I’ll try to debug this, but is there any reason why it was opened here and not in Express? I’m not saying you need to open a new discussion there (I can move it), but it makes me think that without a session this doesn’t happen

[arenddeboer]

Sorry this was indeed supposed to go into the Express repo. Don't put too much time into it, it might well be an issue with my specific setup. For instance I was previously using "source-map-support" which also affected the output, even though removing it did not resolve it.