RangeError: Maximum call stack size exceeded. Why?

Question

    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.

Hi, you seem to be missing some code (I am getting a syntax error) — veryverde
– veryverde, Commented Nov 24, 2021 at 12:32
What happens when you call it with 1? (And how are you calling it?) — doctorlove
– doctorlove, Commented Nov 24, 2021 at 12:32
the thing is this: when i call it the first time, it shows me the right value. but if i try it a second time, i get the error. — eraser
– eraser, Commented Nov 24, 2021 at 12:39

veryverde · Accepted Answer · 2021-11-24 13:01:41Z

2

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) {
  ...
}

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

answered Nov 24, 2021 at 13:01

veryverde

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1 Comment

eraser Over a year ago

worked, thank you!

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