javascript - Shopify Drop down Validation -

i'm building web store on shopify. want add validation dropdown if no size/value selected drop down, automatically select 1st size/value. when click on add cart button.

thanks help.

given html:

<select id="drop">     <option value="0">please select</option>     <option value="1">one</option>     <option value="2">two</option>     <option value="3">three</option> </select> <button id="add">add cart</button> 

use javascript/jquery:

$(document).ready(function() {     var $drop = $("#drop");     $("#add").on("click", function() {         if($drop.val() == 0) {             $drop.val(1);         }     }); }); 

http://jsfiddle.net/82vrccem/1/