title: Zipcode validation remove extra numbers on keyup
body: <p>ik have a input where a zipcode must be checked. This i what i have at the moment.</p>
  
  <pre><code>$("input[id='postal']").keyup(function count() {
  
      var zipcodeValue = this.value;
      zipcodeCheck = zipcodeValue.split(" ").join("");
      var regex = new RegExp(/^[0-9]{4}[a-z]{2}$/i);
  
      if (regex.test(zipcodeCheck) == true) {   
          // something
      } else {
          // something else
      }
  });
  </code></pre>
  
  <p>This is working, but i want to disable user to type more than four numbers.
  The zipcode must be like this 1234AB or 1234 AB but not 12345B.</p>
  
  <p>Can i remove the fifth/sixth number when this is typed on keyup?</p>
  
  <p>Thank you</p>