I have created a search form with RSForm Pro, unfortunately it isn't working.

The concept is to do a TAG Search all the Fields of the Form (Select and Radio) have values which are part of a URL which has to be build when you press on "suchen" (Fields are depending on each other and the button will only show up when all steps have been completed).

I am using this code trying to accomplish this:

function suchen() {
    var URLBase = "http://ego.pc-helfer.eu/index.php?option=com_tags&view=tag";
    var TrailingFixedData = "&types[0]=1";

    finalURL = URLBase + document.getElementsByClassName('value1').value +
    document.getElementsByClassName('value2').value +         
    document.getElementsByClassName('value3').value + 
    document.getElementsByClassName('value4').value + 
    document.getElementsByClassName('value5').value + TrailingFixedData;
}

But when i press "suchen" the Chrome console tells me:
Uncaught ReferenceError: suchen is not defined

I can see the script is being loaded but i still get this message.
url of the Site: http://ego.pc-helfer.eu/produktsuche/substrattkompass