jQuery prevent change for select

Try this:

http://jsfiddle.net/qk2Pc/

var my_condition = true;
var lastSel = $("#my_select option:selected");

$("#my_select").change(function(){
  if(my_condition)
  {
    lastSel.prop("selected", true);
  }
});

$("#my_select").click(function(){
    lastSel = $("#my_select option:selected");
});

If you simply want to prevent interaction with the select altogether when my_condition is true, you could always just capture the mousedown event and do your event prevent there:

var my_condition = true;

$("#my_select").mousedown(function(e){
  if(my_condition)
  {
     e.preventDefault();
     alert("Because my_condition is true, you cannot make this change.");
  }
});

This will prevent any change event from ever occurring while my_condition is true.

In the event someone needs a generic version of mattsven's answer (as I did), here it is:

$('select').each(function() {
    $(this).data('lastSelected', $(this).find('option:selected'));
});

$('select').change(function() {
    if(my_condition) {
        $(this).data('lastSelected').attr('selected', true);
    }
});

$('select').click(function() {
    $(this).data('lastSelected', $(this).find('option:selected'));
});