Question

Here is my code: JS PART

$(document).ready(function(){
    $("#parent").hide();
    $(".parentcheck").click(function(){
            if($(this).val()==="1") 
            {
                $("#parent").show();
                $('#switch').attr('disabled', '');

            }
            else {
                $("#parent").hide();
                $('#switch').attr('disabled', 'disabled');
            }
    });

    $("#switch").change(function () {
    var selectedSwitch = $("#switch").val();
    var parentcheck = $(".parentcheck:checked").val();
    if (selectedSwitch!='' && selectedSwitch!='0'){
    $.ajax({
    type: "POST",
    url : "optionsgenerator.php",
    data: {menu: selectedSwitch},
    success: function(result, status, xResponse){
        if (result!=''){
            if($('#parentcheck').attr('checked')){
                $("#parent").hide();
            }
            else {
                $("#parent").html(result);
                $("#parent").show();
            }
        }
        else{
            alert('Error occured.');
            $("#parent").hide();
        }
    },
    error: function(e){
        alert(e);
    }
    });
    }
    else
    $("#parent").hide();
});

});

And HTML Markup

<select name="switch" id="switch">
<option value="" selected="selected">Select one...</option>
<option value="1">a</option>
<option value="2">b</option>
<option value="0">no one</option>
</select>

<div class="parent">
<input type="radio" class="parentcheck" name="parentcheck" value="0"/>
<input type="radio" class="parentcheck" name="parentcheck" value="1"/>

<select name="parent" id="parent"></select>
</div>

The problems is

If value of radio button with class "parentcheck" is 1, my js shows selectbox without checking if it has something to show (in my case options returned from backend php code) or not

I’m trying to achieve following

If value of radio button with class "parentcheck" is 1 then show
selectbox #parent ONLY if ajax has already returned something, enable selectbox #switch

Answer 1

You are trying to get parentcheck by id, but parentcheck is a class:

var parentcheck = $("#parentcheck:checked").val();

try to change it to

var parentcheck = $(".parentcheck:checked").val();

EDIT:
for the unselecting:

       if($(this).val()==="1") 
        {
            if ($("#parent option").length > 0) {
                 $("#parent").show();
            }
            $('#switch').attr('disabled', '');

        }
        else {
            $("#parent").hide().find('option:selected').removeAttr('selected');
            $('#switch').attr('disabled', 'disabled').find('option:selected').removeAttr('selected');
        }