JQUERY: Check & Uncheck using selection

JQUERY: Check & Uncheck using selection

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<SCRIPT language="javascript">
$(document).ready(function() {

  $("#check").change(function() { 
  	var d = $(this).val();  
  	if(d == 'parent'){
    	$(".child").prop("checked", !d.checked);
	} 
  });

  $("#check").change(function() {
  	var d = $(this).val(); 
  	if(d == 'parentnone'){ 
  	$(".child").prop("checked", false);
  	}
  });
 
});

</SCRIPT>

 <select id="check">
 <option>Select</option>
 <option value="parent" data-checked='false'>All</option>
<option value="parentnone" data-checked='false'> None </option>
</select>
<hr/>

<ul>
  <li>
    <input type="checkbox" class="child" /> Checkbox 1</li>
  <li>
    <input type="checkbox" class="child" /> Checkbox 2</li>
  <li>
    <input type="checkbox" class="child" /> Checkbox 3</li>
</ul>