This is my HTML
<select name="countries" id="countries" MULTIPLE size="8">
   <option value="UK">UK</option>
   <option value="US">US</option>
   <option value="Canada">Canada</option>
   <option value="France">France</option>
   <option value="India">India</option>
   <option value="China">China</option>
</select>
<br />
<input type="button" id="select_all" name="select_all" value="Select All">
When user click on 'Select All' button, I want all the options in the select box to be selected
$('#select_all').click( function() {
    // ?
});
 
     
     
     
     
     
     
     
     
     
     
     
     
    