loader for html control events raised through JavaScript fun

Question

Hi,

 

i developed a page with javascript functions having dropdowns, buttons and checkboxes. when i click on button or change a dropdown value it is taking some time to load data from database.

 

now i want to show some porcessing wheel image in this loading time. when ever a control event raised in the page the processing wheel should be shown until the data loading complete.

 

any help???