Question

Good morning,
as the title suggests, how to run function (JavaScript) when changing the value of a field (no from empty in compiled)?

Answer 1

If you want to check on each key press then

With javascript

<input type="text" id="textbox" onkeyup="TextBoxChanged()" />

function TextBoxChanged(){
   alert("changed");
}

With jquery

This requires you to import jquery file to be imported in the web page.

Live Demo

$(document).ready(function(){
  $('#textbox').keyup(function() {
      alert("changed");
  });​
});

Bind change event with textbox, this will cause event when textbox loses focus.

<input type="text" id="textbox" />
$(document).ready(function(){
   $('#textbox').change(function(){
      alert("changed");
   });
});