const http = require('http');
const fs = require('fs');
const url = require('url');
const hostname = 'xxxx';
const port = xxxx;


const server = http.createServer((req, res) => {
    let parsedUrl = url.parse(req.url, true);
    var qdata = parsedUrl.query;
    let n = parseInt(qdata.n);
    console.log(n);
    if (n <= 0) {
        res.writeHeader(500, {
            'Content-Type': 'text/plain',
        });
        res.write("Fuer n wurde kein gueltiger Parameter uebergeben!");
    }
    else {
        res.writeHeader(200, {
            'Content-Type': 'text/plain',
        });
        function fibonacci(num) {
  if (num <= 1) return 1;

  return fibonacci(num - 1)   fibonacci(num - 2);
}
        res.write("Die "   n   "-te Fibonacci Zahl lautet "   fibonacci(n));
    }


    res.end();
});

server.listen(port, hostname, () => {
    console.log(`Server running at http://${hostname}:${port}/`);
});

if i run this code, i get the error RangeError: Maximum call stack size exceeded. But why? It happened when i called it with 9, fibonacci shouldnt be a problem at such a small number.

CodePudding user response：

There are two problems here: 1. getting it to run, 2. getting it to run properly.

1. You are incorrectly parsing data, such that let n = parseInt(qdata.n); gives you back undefined. The callback is the function that is executed once the server starts. This means that even before you have inputted a number, your server is running the fibonacci sequence.

Because it's already parsing data, it parses n, which, of course, is undefined. Parsing this into an Int, you get NaN. This is a problem because Nan-1 or Nan-2 always returns Nan, meaning that you enter into an infinite upon start of the server.

To fix this, you should check whether n exists:

if(String(n) !== String(NaN) {
  ...
}

2. Efficiency: calculating the fibonacci sequence like this will cause a huge problems down the line. I would take a look at dynamic programming.

CodePudding user response：

Maybe qdata.n is undefined.

parseInt(undefined) is NaN (Not a Number)

parseInt(undefined) <= 1 is false

So it loops endlessly.

Same for:

parseInt(null) is NaN

parseInt('') is NaN

Just check:

    let n = parseInt(qdata.n);
    console.log(n);
    if (!Number.isNaN(n) && n <= 0) {
        // ...