Hey guys, i'm fairly new to programming in Javascript.
I've been trying to write a basic user name and password program.
I was wondering if I could get some help with how I would put it in a loop so if the information in incorrect, it will prompt up "x" amount of times until the information is correct. Thanks, here's what I have so far.

var user_name = prompt ("Please enter your username: ");
var password = prompt ("Please enter your password: ");

if( (user_name=="John123") && (password=="helloworld") ){
alert("Welcome, " + user_name + ".");
alert (" Sorry, information invalid. " );