the  ID attribute of a HTML element and looks similar to this: TopZone_g_d72e1f89_87e6_4f08_b6c5_165dc560ce8a_ _ctl1 TopZone defines the location of the Web Part, along with its GUID . The bold part ( _ctl1 ) denotes the ID of the control in question, a SELECT in my case. The JavaScript code to add an