script error encountered, _doPostBack is undefined issue

The case I have is as the following. I am developing a web page using VS2013 with .Net 4.5.1, C#, and IE11. I have three html radio buttons and four html select controls. The data for adding to the first HTML select is retrieved from the SQL DB on initial page load. The first HTML select options will be populated when one of three html radio buttons is selected. Supposedly, a single record for the second html select should be retrieved from the table after the first html select is selected. The second html select options will be added afterwards. The problem is that I had the above problem when I called _doPostBack in my JavaScript function. My question is that there is any other alternative ways to get this function done since I spent a lot time to resolve this _doPostBack issue and to retrieve the data at the server side. My the other problem ...