I'm trying to set focus to various fields when users neglect to enter required information. It works great on textbox fields, but not on dropdown lists.

Here's the code I'm using:

if (showingDate == null || showingDate == '')  {   alert('Please enter a Showing Date (Scheduled), or change the Reason for the Call to Property Question.');   document.getElementById('custevent_showing_date_scheduled').focus();  }    else if (showingTimeStart == null || showingTimeStart == '')  {   alert('Please enter a Showing Start Time (Scheduled), or change the Reason for the Call to Property Question.');   document.getElementById('custevent_showing_time_scheduled').focus();  }    else if (showingTimeEnd == null || showingTimeEnd == '')  {    alert('Please enter a Showing End Time (Scheduled), or change the Reason for the Call to Property Question.');   document.getElementById('custevent_showing_end_time').focus();  }    return false;