Front-End Web Development: The Big Nerd Ranch Guide

Handling Failures with then

then accepts a second argument, which is invoked when the Deferred shifts to the rejected state. To see this in action, add a second function argument (making sure to add a comma between the two function arguments) to formHandler.addSubmitHandler in main.js. Inside of this function, show an alert with a simple error message.

...
  formHandler.addSubmitHandler(function (data) {
    myTruck.createOrder.call(myTruck, data)
      .then(function () {
        checkList.addRow.call(checkList, data);
      },
      function () {
        alert('Server unreachable. Try again later.');
      }
      );
  });
...

At the top of main.js, misspell the server name so that Ajax requests fail. (This change will only be temporary, so you may want to simply cut a section out ...