AngularJS ng-app Directive
The AngularJS ng-app specifies that it is the root element of the AngularJS application. All AngularJS application must contain a root element. You can only have one ng-app directive in your HTML document. If you have more than one ng-app directive; the first appeared directive will be used.
modulename: It is an optional parameter. It specifies the name of a module that you want to add with the application.
See this example:Test it Now
Note: ng-app is the simplest, easiest and most common way to bootstrap an application.