jquery for multiple select box of select html code example

Example 1: how to choose multiple option from select option

<!-- JUST ADD multiple ATTRIBUTE WITHIN select ATTRIBUTE -->
Cars:<br>
<select name="car" multiple>
    <option value="Volvo">Volvo</option>
    <option value="Thar">Thar</option>
    <option value="Audi">Audi</option>
</select>

Example 2: jquery select2 multiple select all

$("#checkbox").click(function(){
    if($("#checkbox").is(':checked') ){
        $("select > option").prop("selected","selected");
    }else{
        $("select > option").removeAttr("selected");
     }
});