You've used getElementById. To make this work you have to add id attribute in you input and select fields.
<select name='transType' id="transType">
<input type='number' name='transID' style='width: 75%;' id="transID"/>
Secondly instead of using top.location.href you can use these two built in Netsuite functions
nlapiResolveURL ( type , subtype , id , pagemode )
nlapiSetRedirectURL ( type , subtype , id , pagemode , parameters )