Flush tampermonkey changes - tampermonkey

Question

I am trying to create a Tampermonkey script to automatically fill a login form with my username and password and then I would like to click the login button. However, with the code below, it appears to wait the three seconds, and THEN it fills the text into the boxes. How can I "flush" the changes so that they appear before the wait time occurs?
Thanks!
(function() {
'use strict';
function wait(ms){
var start = new Date().getTime();
var end = start;
while(end < start + ms) {
end = new Date().getTime();
}
}
window.onbeforeunload = function (){
return "Leaving page...";
}
$(document).ready(function() {
document.getElementById("username").value = "userValue";
document.getElementById("password").value = "passwordValue";
wait(3000);
document.getElementsByClassName("btn-large").click();
});
})();

Answer 1

That wait function is locking up the browser tab (and probably the browser, and potentially the whole computer). Don't code like that!
Also:
(function() {... is completely superfluous in a Tampermonkey script.
$(document).ready(function()... is not helpful except in rare cases that do not apply here.
Lots, lots more, etc...
Here's that code refactored:
window.onbeforeunload = function () {
return "Leaving page...";
}
//-- Hacker easter egg! See linked questions.
document.getElementById ("username").value = "userValue";
document.getElementById ("password").value = "passwordValue";
setTimeout (clickBtnAfterDelay, 3000);
function () {
//-- Brittle! See linked questions.
document.getElementsByClassName ("btn-large")[0].click ();
}