how to avoid duplicate values in dropdownlist using jquery

1$(".select option").val(function(idx, val) {
2  $(this).siblings('[value="'+ val +'"]').remove();
3});

1<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
2
3<select class="select">
4  <option value="">All</option>
5  <option value="com">.com 1</option>
6  <option value="net">.net 1</option>
7  <option value="com">.com 2</option> <!-- will be removed since value is duplicate -->
8  <option value="net">.net 2</option> <!-- will be removed since value is duplicate -->
9</select>