Why does this Fibonacci number function return infinity for the 4000th value?

Question

function fibo() {
var first,second,add;
for(var i=0;i<4000;i++){
    if(i === 0){
        first = 1;
        second = 2;
    }
    add = first + second;
    first         


        

Answer 1

You can use WebWorkers and BigInt to calculate huge values of the fibonacci sequence:

var input = document.querySelector('input');
var output = document.querySelector('#output');
var fulloutput = document.querySelector('#fulloutput');
var time = document.querySelector('#time');
var start, end;
var worker;

var createWorker = function () {
  if (worker) worker.terminate();
  var workerContent = "self.onmessage = " + workerFunction.toString();
  var blob = new Blob([workerContent], {type: 'application/javascript'}); 
  worker = new Worker(URL.createObjectURL(blob));
  worker.onmessage = receive;
};

var workerFunction = function(event) {
  var total = BigInt(event.data);
  var fib = function(index) {
    var temp;
    var last = BigInt(0);
    var sum = BigInt(1);
    for (; index >= BigInt(2); index--) {
      if (index % BigInt(1000) === BigInt(0)) 
        self.postMessage({
          total: total,
          calculating: index
        });
      temp = last;
      last = sum;
      sum += temp;
    }
    return sum;
  };
  if (total > BigInt(0)) self.postMessage({done: fib(total)});
  else self.postMessage({error: 'Input error'});
};

window.addEventListener('load', function () {
  if (!window.Worker || 
      !window.Blob   || 
      !window.URL    || 
      !window.BigInt) {
    output.textContent = 'Browser not supported'; 
  } else {
    start = performance.now();
    createWorker();
    output.textContent = 'Worker created, starting calculations';
    worker.postMessage(input.value);
    input.addEventListener('change', function () {
      createWorker();
      start = performance.now();
      output.textContent = 'Calculating';
      worker.postMessage(input.value);
    });
  }
});

var receive = function(event) {
  if (event.data.error) {
    output.textContent =  event.data.error;
  }
  if (event.data.calculating) {
    var total = BigInt(event.data.total);
    var index = BigInt(event.data.calculating);
    var progress = (BigInt(100) * (total - index) / total);
    output.textContent = 'Calculating ' + progress + '%';
  } 
  if (event.data.done) {
    var formatter = new Intl.NumberFormat('en', {
      notation: 'scientific'
    });
    output.textContent = formatter.format(event.data.done);
    fulloutput.textContent = event.data.done;
    end = performance.now();
    time.textContent = 'It took ' + ((end - start) / 1000) + ' seconds';
  }
};

body {
  display: grid;
  place-content: center;
  min-height: 100vh;
}
p, pre  {
  text-align: center;
  width: 80vw;
  white-space:normal;
  word-wrap: break-word;
}

N: