jQuery: How to capture the TAB keypress within a Textbox

Working example in jQuery 1.9:

$('body').on('keydown', '#textbox', function(e) {
    if (e.which == 9) {
        e.preventDefault();
        // do your code
    }
});

Edit: Since your element is dynamically inserted, you have to use delegated on() as in your example, but you should bind it to the keydown event, because as @Marc comments, in IE the keypress event doesn't capture non-character keys:

$("#parentOfTextbox").on('keydown', '#textbox', function(e) { 
  var keyCode = e.keyCode || e.which; 

  if (keyCode == 9) { 
    e.preventDefault(); 
    // call custom function here
  } 
});

Check an example here.

$('#textbox').live('keypress', function(e) {
    if (e.keyCode === 9) {
        e.preventDefault();
        // do work
    }
});