Dialog Code

dialog.js

  Office.context.ui.displayDialogAsync('https://localhost:3000/function-file/dialog.html',
      { height: 20, width: 30, displayInIframe: true },
      function (asyncResult) {
          dialog = asyncResult.value;
          // callbacks from the parent
          dialog.addEventHandler(Office.EventType.DialogEventReceived, processMessage);
          dialog.addEventHandler(Office.EventType.DialogMessageReceived, processMessage);
      });