ngApp (directive in module ng )

Use this directive to auto-bootstrap on application. Only one directive can be used per HTML document. The directive designates the root of the application and is typically placed ot the root of the page.

In the example below if the ngApp directive would not be placed on the html element then the document would not be compiled and the {{ 1+2 }} would not be resolved to 3.

ngApp is the easiest way to bootstrap an application.

Source

Demo