JQuery - OnKeyUp
HTML
http://api.jquery.com/keyup/
<br> <br />Type Here:<input type="text" id="textbox1"/>
<br><br>
Results
<br /><input type="text" id="textbox2"/>
<br /><input type="text" id="textbox3"/>
<br /><br /><br />
<div id="log"></div>
JavaScript
$("#textbox1").keyup(function(){
var textinput = $('#textbox1').val().substring(0,8);
$('#log').append('<br />Handler for .keyup() called - ' + textinput);
$("#textbox2").val(textinput);
$("#textbox3").val(textinput);
});