JSFiddle - React, Tailwind, and code Playground

JavaScript

function Max(num1, num2, num3) {
    var largest;
    if ((num1 > num2) && (num1 > num3)) {
        largest = num1;
    } else if ((num2 > num1) && (num2 > num3)) {
        largest = num2;
    } else {
        largest = num3;
    }
    return largest;
}

var num1 = prompt("Enter first number", " ");
var num2 = prompt("Enter second number", " ");
var num3 = prompt("Enter third number", " ");

document.body.innerHTML += 'Without parseInt():' + Max(num1, num2, num3) + '<br>';

document.body.innerHTML += 'With parseInt():' + Max(parseInt(num1, 10), parseInt(num2, 10), parseInt(num3, 10)) + '<br>';

document.body.innerHTML += '<br>Other examples: <br>';

document.body.innerHTML += Max(5, 21, 100) + '<br>';
document.body.innerHTML += Max(10, 24, 5) + '<br>';