I understand that Express resides on the server and Angular resides on the client but, as far as I know, Angular can do everything that Express can do which is
There is lot of stuff that one wants to control from server. And that is the place where the server side frameworks come into picture.
An web app is not just some html pages linked together. There are lot of other things that needs to be implemented
and other such thing require a server framework. So as mentioned earlier the client side frameworks like AngularJS complement server side frameworks.