Select a state from this menu:

Once a state has been selected, the multiple select list below will be populated with a partial list of ZIP code names drawn from a database of html files that are loaded via a hidden IFRAME. (ZIP code data drawn from sources on the US Census Bureau site).

Selecting a state from the drop down menu invokes the callToServer() function, which, instead of calling a single script on the server, loads into our hidden IFRAME one of 51 HTML files which contain ZIP code data for each of the 50 states (plus DC). The onload event of these files calls the handleResponse() function, which parses out the data in the loaded file and inserts new option elements into a multiple SELECT list.