How To Use JQuery On Dynamically Created Textbox

i am creating Textboxes at Runtime with something like this

Code:
Dim cnt As New TextBox
cnt.ID = "cont_" & x
If multiline Then
cnt.TextMode = TextBoxMode.MultiLine
End If

These are dynamically created fields. so what i want to do is to use this following JQuery on this textbox

Code:
$(document).ready(function() {
$("#contentbox").keyup(function() {
var box=$(this).val();
var main = box.length *100;
var value= (main / 145);
var count= 145 - box.length;
if(box.length <= 145) {
$('#count').html(count);
$('#bar').animate({"width": value+'%',}, 1);
}
return false;
});
});

and what this function does it count the number of Characters that have been typed in a Textbox. so i am displaying the remaining characters. So that is working fine on my example because the Element is known at Early Binding. Now my question is what if the textbox is created dynamically ?

Code:

contentbox

this is the name of the Textbox in my example. how do we use a J Query in Dynamically created Textbox.