Block Mac navigation when form has changed

block_mac_nav.js

  function blockLeaving (e){
      if(e.metaKey && (e.keyCode == 39 || e.keyCode == 37)){
          switch(document.activeElement.tagName){
              case "INPUT":
              case "TEXTAREA":
                  break;
              default:
                  if(!window.confirm("You have unsaved changes. Are you sure you want to leave the page?")){
                      e.preventDefault();
                  }
                  return false;
          }
      }
  }
  function detectChange (e){
      if(!this.fired){
          document.body.addEventListener("keydown", blockLeaving);
          this.fired = true;
      }
  }

  var formElements = document.querySelectorAll("input, textarea, select, button");
  for(var n=0; n < formElements.length; n++){

      switch(formElements[n].tagName){
          case "INPUT":
          case "TEXTAREA":
              formElements[n].addEventListener("input", detectChange);
              break;
          case "SELECT":
              formElements[n].addEventListener("change", detectChange);
              break;
      }

  }