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Uncaught exception causes Express to set to undefined basic request parameters #5842
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Looks like a problem with the event you are handling the event
finish. if we check the documentation this event:Emitted when the response has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the operating system for transmission over the network.
so I'm guessing that in this logical scope it is no longer possible to access the object property you want. And that is why you receive an undefined.
If you change
finishtoendeverything work as you expected.Hi @NicoAdrian 👋
I think the uncaught exception in Node causes a crash unless properly handled. And trying to access the
req.paramsafter that uncaught exception will be unpredictable because the request life cycle is not the same.I would add a global error handler,
app.use((err, req, res, next) => { console.log("error handler: " + err.message); res.status(500).send("Something broke!"); });
Looks like a problem with the event you are handling the event
finish. if we check the documentation this event:Emitted when the response has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the operating system for transmission over the network.
so I'm guessing that in this logical scope it is no longer possible to access the object property you want. And that is why you receive an undefined.
If you change
finishtoendeverything work as you expected.The
reqexpress (or is it ?) object is still accessible, with many properties. But the propertyparams(also thebaseUrlproperty for instance).The
endandfinishevents serve different purposes:endis related to the end of reading data from the incoming requestfinish(what I want) is related to the completion of writing data to the outgoing response (writable stream)
Scope shouldn't be an issue: I still have the
req.paramsin scope. I go back to my first question: Why is it cleared by express ? (or NodeJS ?)Hi, It is not cleared by Express or Nodejs, rather depends on the request life-cycle. Please allow me to clear it out a few hours later, I am currently not in front of my computer.
PS: Please allow me to convert this to a discussion, if the need arises, we will revert this back to issue.
Consider this code:
curl http://localhost:3000/foo/blablablawill cause Express to:==>
TypeError: Cannot read properties of undefined (reading 'bar')After the uncaught exception,
req.paramsisundefined(among other req parameters, not listed here). Thus, trying to accessbarfromundefinedis also an exception, causing the server to crash and terminate.Looks like Express "clears" some variables in the
reqobject.