I'm using codes below to set value attributes to null but they only work for input fields. How can I do same thing for select boxes? When I clone, the first option (Select unit) should be selected.
VER 1:
var $cloned = $('#unit-field-cover div:last').clone();
$('#unit-field-cover div:last').after($cloned);
$('#unit-field-cover div:last select').attr({name:"size-unit[]", value:''});
HTML
<select name="size-unit[0]">
<option value="">Select unit</option>
<option value="Inches" selected="selected">Inches</option>
<option value="Centimeters" >Centimeters</option>
<option value="N/a">N/a</option>
</select>