Javascript no added css class

Question

// Css class add hoy na please help me
//Code check please
//Problem thank solution korean please

var name = prompt('your name');
var name2 = ('shorif shuvo');
var names = (name + '<br>');

var password1 = parseInt(prompt("your password"));
var password2 = parseInt(prompt('confirm password'));

if (password1 === password2) {
for (var i = 0; i < 10; i++) {
document.write(names);
}

}
else {
document.write('Are you bad boy');
}

var bg = document.getElementsById("bg");

if (name2 == name) {
bg.classList.add("bd");
}
/* class not add please help me */

Answer 1

class is added, but document.write open a new document, so css are deleted...

you must either assign document.body.innerHTML, or dynamically document.write css (inside <style> tag) :

document.body.innerHTML += "appended to body content";

Answer 2

CSS CODE
body {
font-size: 30px;
font-weight: 500;
}
.bg{
background-image: url("../images/img-profile.jpg");
color: white;
}