You can do in both ways. Using ajax and using the normal form posting approach.

With ajax

<input type="button" id="btnAdd" value="Add" />

and in your javascript

$("#btnADd").click(function(){

   $.post("yourcontroller/youraction?"+prod="+$("hdnProductId").val()+"&qty="+$("txtQty").val(),function(data){

     //Do with the response data

  });

});

You can add the new item to tge kof available items in javasrtipt itseld using the jQuery append() method or you can do a get call fro a partia view which lists all the products.