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

For better results you can use the jsperf.com: http://jsperf.com/fib-vs-fib-loga/

Just a lite change in the function to get the max position possible to calculate by javascript.

Yes, the result will be diferent on each browser and arch bean used.

function fibo() {
    var first,second,add;
    for(var i=0;i<4000;i++){
        if(i === 0){
            first = 1;
            second = 2;
        }
        if(first+second > Number.MAX_VALUE){
            console.debug(i, first, second);
            return;
        }
        add = first + second;
        first = second;
        second = add;
    }
    alert(add);
}
fibo();

The result is: 1473 8.077637632156222e+307 1.3069892237633987e+308 Where 1473 is the maximum fibonacci position possible to calculate with javascript.