You could use addEventListener to add as many listeners as you want.
document.getElementById("Save").addEventListener('click',function ()
{
alert("hello");
//validation code to see State field is mandatory.
} );
Also add script tag after the element to make sure Save element is loaded at the time when script runs
Rather than moving script tag you could call it when dom is loaded. Then you should place your code inside the
document.addEventListener('DOMContentLoaded', function() {
document.getElementById("Save").addEventListener('click',function ()
{
alert("hello");
//validation code to see State field is mandatory.
} );
});