jquery find class and get the value

Class selectors are prefixed with a dot. Your .find() is missing that so jQuery thinks you're looking for <myClass> elements.

var myVar = $("#start").find('.myClass').val();

var myVar = $("#start").find('.myClass').first().val();

var myVar = $("#start").find('myClass').val();

needs to be

var myVar = $("#start").find('.myClass').val();

Remember the CSS selector rules require "." if selecting by class name. The absence of "." is interpreted to mean searching for <myclass></myclass>.