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

Because Number.MAX_VALUE + Number.MAX_VALUE === Infinity

The issue is that sum exceeds JavaScripts capabilities for storing numeric values.