How to show the “Are you sure you want to navigate away from this page?” when changes committed?

Question

Here in stackoverflow, if you started to make changes then you attempt to navigate away from the page, a javascript confirm button shows up and asks: \"Are you sure you want

Answer 1

here is my html

 
    

        Welcome To My Home
    
    

        I am a student at Columbia College of Missouri.
    

And so this is how I did something similar in javaScript

var myGlobalNameHolder ="";

function myFunction(){
var myString = prompt("Enter a name", "Name Goes Here");
    myGlobalNameHolder = myString;
    if (myString != null) {
        document.getElementById("replaceME").innerHTML =
        "Hello " + myString + ". Welcome to my site";

        document.getElementById("belong").innerHTML =
        "A place you belong";
    }   
}

// create a function to pass our event too
function myFunction2(event) {   
// variable to make our event short and sweet
var x=window.onbeforeunload;
// logic to make the confirm and alert boxes
if (confirm("Are you sure you want to leave my page?") == true) {
    x = alert("Thank you " + myGlobalNameHolder + " for visiting!");
}
}