Project: survey
Task (moderate): Class NpsQuestion (file 'common/NpsQuestion.js') inherits from Question. Its constructor params are: title (string), name (string), preview (boolean). Add a button (class 'add-nps') in 'common/SurveyDesign.js', and click it to create a NpsQuestion (random title, unique name) whose root is prepended the form. In preview page, highlight the clicked score option (class 'option'), and store score (0-10) in param-named control.