In that case if, for example, you have question codes Q1, Q2, Q3, disable AJAX in the survey theme options and place a script like this in the source of Q2:
Code:
<script type="text/javascript" charset="utf-8">
$(document).on('ready pjax:scriptcomplete',function(){
// Define the previous answer(s)
var q1Value = '{Q1}';
// Identify the drop-down
var thisSelect = $('#question{QID} select.form-control:eq(0)');
// Reset the drop-down if its value equals previous answer(s)
if(thisSelect.val() == q1Value) {
if($('option[value=""]', thisSelect).length == 0) {
$(thisSelect).prepend('<option value="">Please choose...</option>');
}
thisSelect.val('');
}
// Remove drop-down option
$('option[value="'+q1Value+'"]', thisSelect).remove();
});
</script>
Place a script like this in the source of Q3:
Code:
<script type="text/javascript" charset="utf-8">
$(document).on('ready pjax:scriptcomplete',function(){
// Define the previous answer(s)
var q1Value = '{Q1}';
var q2Value = '{Q2}';
// Identify the drop-down
var thisSelect = $('#question{QID} select.form-control:eq(0)');
// Reset the drop-down if its value equals previous answer(s)
if(thisSelect.val() == q1Value || thisSelect.val() == q2Value) {
if($('option[value=""]', thisSelect).length == 0) {
$(thisSelect).prepend('<option value="">Please choose...</option>');
}
thisSelect.val('');
}
// Remove drop-down options
$('option[value="'+q1Value+'"]', thisSelect).remove();
$('option[value="'+q2Value+'"]', thisSelect).remove();
});
</script>
Sample survey attached: