Find the upper bound of this factorial function or optimized code

Question

I wrote a function to find the factorial and count the number of trailing zeros for the given input function. I wrote it in Javascript programming language. It gave me the correct answer till the input is 21, but after which it cannot calculate(Thinking I have reached my function upper bound). Can someone explain/give me optimized code to find trailing zeros till the input is 10,000 or more. Else is any other mathematical method to calculate? writing my code here.

function factorial(n) {
    var fact = 1;
    var value = "";
    var count = 0;
    for (var i = n; i > 1; i--) {
        value = value+(i+"*");
        fact = fact*i;
    }

    console.log(value + i + "=", fact);

    for (var i = n; i > 1; i--) {
        if (fact%10 === 0) {
            count++;
            fact = fact/10;
        }
    }

    console.log(count);
}