This extra code is required in this web script to create a custom event that is triggered when a user clicks on a button in the title bar. The <@createWidgets> directive is able to pass a reference to the editDashletEvent object by way of a special data structure that can be used when creating the instantiation metadata in the JavaScript controller.
The problem is that when creating the model it is impossible to distinguish between a primitive String and a String that is a reference to a JavaScript variable defined in the FreeMarker template, because the controller has no awareness of that variable (the JavaScript controller is processed before the FreeMarker template).
To work around this problem the webview.get.js controller sets a reference by including the following object to the widget’s options metadata object:
eventOnClick: { _alfValue : "editDashletEvent", _alfType: "REFERENCE"},
When the <@createWidgets> directive encounters a JSON object with the attributes _alfValue and _alfType, and only those attributes, it converts that object into a variable reference instead of a String.