Hey, how can I find in my array what value is duplicate and how many times it is ? In js [duplicate]

This is how my array get value

var output = [];
function FizzBuzz() {
    for(var count = prompt("Type the number:"); count >= 1; count--) {
        if(count % 3 === 0 && count % 5 === 0) {
            output.push("FizzBuzz");
        }
    }
}

My user input an certain number and I want to display how many times he get “fizzbuzz”