How to disable buttons when nothing is selected in the list boxes

Question

I'm new to jquery & I tried some codes to disable the buttons. But, Its not working for me.
I want to enable the "Add category" button only if any three values(one value per each box) are selected from the above three boxes and I want to enable the "Remove Category" & "Save Categories" button only if there is any values in the fourth box.

var one = $('.select-manage-category').val();
var two = $('.select-manage-category1').val();
var three = $('.select-manage-category2').val();
$('#add-category').click(function() {
  $(
    '.select-manage-category, .select-manage-category1, .select-manage-category2'
  ).each(function() {
    $('#selected-lst-values').append('<option value="' + $(this).val() + '">' + $(this).val() + '</option>');
  });
});
$('#remove-category').click(function() {// check change here
  var select = document.getElementById('selected-lst-values');
  
    for(var i=0;i<3;i++){
      select.removeChild(select.lastChild);
    }
});
$('#selected-lst-values>option').on("change",function(){
		if($(this).val()===''){
		$('#mnage-category-savebtn').attr({disabled:disabled});
		
	}
	else{
		$('#mnage-category-savebtn').removeAttr('disabled');
	}
	})

.select-manage-category,
.select-manage-category1,
.select-manage-category2 {
  width: 100px;
  float: left;
  margin-right: 4px;
}

p {
  clear: left;
  text-align: center;
}

#selected-lst-values {
  width: 100%;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div><select class="form-control select-manage-category" size="5">
    <option>1</option>
    <option>2</option>
    <option>1</option>
    <option>2</option>
</select></div>

<div><select class="form-control select-manage-category1" size="5">
    <option>1</option>
    <option>2</option>
    <option>1</option>
    <option>2</option>
		</select></div>
<div><select class="form-control select-manage-category2" size="5">
    <option>1</option>
    <option>2</option>
    <option>1</option>
    <option>2</option>
		</select>
</div>
<p class="text-center color-red">You can add up to 20 categories</p>
</div>
<input id="add-category" name="add" type="button" value="Add Category" disabled>
<input id="remove-category" name="add" type="button" value="Remove Category" disabled>
<div><select id="selected-lst-values" class="form-group percent-100" size="5">
		</select></div>
<button class="btn btn-md btn-radius pi-btn prodetails-btn" type="button" disabled><strong>Save Categories</strong> 
    <span class="glyphicon glyphicon-menu-right right-arrow-head-icon"></span>
</button>

Answer 1

You need to add change event to all three select-manage-category list and your selected-lst-values list as shown in the snippet!

Hope that answers your question!

var one = $('.select-manage-category').val();
var two = $('.select-manage-category1').val();
var three = $('.select-manage-category2').val();


$('.select-manage-category, .select-manage-category1, .select-manage-category2').change(function() {
  var one = $('.select-manage-category').val();
  var two = $('.select-manage-category1').val();
  var three = $('.select-manage-category2').val();
  if (one && two && three) {
    $("#add-category").prop("disabled", false);
  } else {
    $("#add-category").prop("disabled", true);
  }

});

$('#selected-lst-values').change(function() {
  if ($(this).val()) {
    $('#remove-category').prop("disabled", false);
    $('#save-categories').prop("disabled", false);
  } else {
    $('#remove-category').prop("disabled", true);
    $('#save-categories').prop("disabled", true);
  }
});

$('#add-category').click(function() {
  $(
    '.select-manage-category, .select-manage-category1, .select-manage-category2'
  ).each(function() {
    $('#selected-lst-values').append('<option value="' + $(this).val() + '">' + $(this).val() + '</option>');
  });
});
$('#remove-category').click(function() { // check change here
  var select = document.getElementById('selected-lst-values');

  for (var i = 0; i < 3; i++) {
    select.removeChild(select.lastChild);
  }
    if ($('#selected-lst-values').val()) {
    $('#remove-category').prop("disabled", false);
    $('#save-categories').prop("disabled", false);
  } else {
    $('#remove-category').prop("disabled", true);
    $('#save-categories').prop("disabled", true);
  }



});
$('#selected-lst-values>option').on("change", function() {
  if ($(this).val() === '') {
    $('#mnage-category-savebtn').attr({
      disabled: disabled
    });

  } else {
    $('#mnage-category-savebtn').removeAttr('disabled');
  }
});

.select-manage-category,
.select-manage-category1,
.select-manage-category2 {
  width: 100px;
  float: left;
  margin-right: 4px;
}

p {
  clear: left;
  text-align: center;
}

#selected-lst-values {
  width: 100%;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div><select class="form-control select-manage-category" size="5">
    <option>1</option>
    <option>2</option>
    <option>1</option>
    <option>2</option>
</select></div>

<div><select class="form-control select-manage-category1" size="5">
    <option>1</option>
    <option>2</option>
    <option>1</option>
    <option>2</option>
		</select></div>
<div><select class="form-control select-manage-category2" size="5">
    <option>1</option>
    <option>2</option>
    <option>1</option>
    <option>2</option>
		</select>
</div>
<p class="text-center color-red">You can add up to 20 categories</p>
</div>
<input id="add-category" name="add" type="button" value="Add Category" disabled>
<input id="remove-category" name="add" type="button" value="Remove Category" disabled>
<div><select id="selected-lst-values" class="form-group percent-100" size="5">
		</select></div>
<button id='save-categories' class="btn btn-md btn-radius pi-btn prodetails-btn" type="button" disabled><strong>Save Categories</strong> 
    <span class="glyphicon glyphicon-menu-right right-arrow-head-icon"></span>
</button>