How does nodejs handle multiple request?

[Temepest74]

I read some documentations about how nodejs handle different requests from multiple users at once, but I cannot get my head around it without examples. So I have a question about the next code.

app.get('/oauth-callback', async (req, res) => 
{
  try {
    //get temporary auth code
    const responseBody = await axios.post('https://example.com/token');
    const userData = await axios.get(''https://example.com/token-2');

    const accessToken = responseBody.data.access_token;
    const refreshToken = responseBody.data.refresh_token;
    const expiresAt = responseBody.data.expires_in;

    //do smth with this data which may take some time
    });
    res.redirect('/'); //try to find where to redirect
  } catch (e) {
    console.error(e.message);
  }
})

Let's assume a user (A) and another user (B) access this endpoint at the same time. Is there a risk of user B changing the responseBody of user A? If so, when and why? Both requests to token and token-2 will give unique responses to each user.

[RaisinTen]

I think it will be more helpful if you could share some code that runs with no errors. Also, responseBody is const + not modified in the code + it is not even shared with the callback called when a different user requests the server.

[Temepest74]

I shared a small modified part of it due to NDA with my company.
Maybe rephrasing my question will help. Is there any risk of data (not a const one) being compromised inside an async function if too many requests at the same endpoint (in my case: oauth-callback) happen at the same time?

[RaisinTen]

No, because the callbacks are executed sequentially. Here is a demonstration:
Here is an http server to log and increment a variable in an async callback for each request:

const http = require('http');

let data = 1;

http.createServer(async(req, res) => {
  console.log(data++);
  res.end();
}).listen(5000);

Here is a bash script to send 1000 requests to the server simultaneously:

#!/bin/bash

for i in {1..1000}
do
    curl localhost:5000&
done

When you run the two, you'll see the server log the numbers 1 to 1000. If anything were to go wrong with the data in the async http callbacks, data wouldn't be incremented as expected. That doesn't happen because these run in a single thread though the requests come in parallel.

[Temepest74]

Thank you