title: Check for empty field on form submission
body: <p>I have create an eshop. 
  I have enter an input field for 'quantity' and When i click on a submit button the products will be added in my basket. But if i press the submit button with empty the quantity field it will redirect me to an empty page. </p>
  
  <p>So I want to attach an event to the form submission so that nothing is done if the quantity field is empty.</p>
  
  <p>New in javascript, Thanks in advance!</p>