How does NodeJS process multiple GET requests from different users/browsers?

Question

I'd like to know how does NodeJS process multiple GET requests from different users/browsers which have event emitted to return the results? I'd like to think of it as each time a user executes the GET request, it's as if a new session is started for that user.

For example if I have this GET request

var tester = require('./tester-class');

app.get('/triggerEv', async function(req, res, next) {
    // Start the data processing
    tester.startProcessing('some-data');

    // tester has event emitters that are triggered when processing is complete (success or fail)
    tester.on('success', function(data) {
        return res.send('success');
    }
    tester.on('fail', function(data) {
        return res.send('fail');
    }
}

What I'm thinking is that if I open a browser and run this GET request by passing some-data and start processing. Then open another browser to execute this GET request with different data (to simulate multiple users accessing it at the same time), it will overwrite the previous startProcessing function and rerun it again with the new data.

So if multiple users execute this GET request at the same time, would it handle it separately for each user as if it was different and independent sessions then return when there's a response for each user's sessions? Or will it do as I mentioned above (this case I will have to somehow manage different sessions for each user that triggers this GET request)?

I want to make it so that each user that executes this GET request doesn't interfere with other users that also execute this GET request at the same time and the correct response is returned for each user based on their own data sent to the startProcessing function.

Thanks, I hope I'm making sense. Will clarify if not.

Answer 1

If you're sharing the global tester object among different requests, then the 2nd request will interfere with the first request. Since all incoming requests use the same global environment in node.js, the usual model is that any request that may be "in-flight" for awhile needs to create its own resources and keep them for itself. Then, if some other request arrives while the first one is still waiting for something to complete, then it will also create its own resources and the two will not conflict.

The server environment does not have a concept of "sessions" in the way you're using the term. There is no separate server-session or server state that each request lives in other than the request and response objects that are created for each incoming request. This is not like PHP - there is not a whole new interpreter state for each request.

I want to make it so that each user that executes this GET request doesn't interfere with other users that also execute this GET request at the same time and the correct response is returned for each user based on their own data sent to the startProcessing function.

Then, don't share any resources between requests and don't use any objects that have global state. I don't know what your tester is, but one way to keep multiple requests separate from each other is to just make a new tester object for each request so they can each use it to their heart's content without any conflict.