Web app using javascript frameworks VS usual method? Confused

I have been learning programming from a year npow. I really don't fully understand the WEB and Web Development. I came to know that nowadays all the web applications are evolved to a different state unlike ordinary web application built using HTML, CSS, javascript + a server(PHP). So nowadays the web apps are on the client side. That means the total application is on client side built witha a javascript framework such as AngularJs or Emberjs.

So what my question is, what is new with this approach? How does it differ from an old days web application in which the view is in the client side and all the other application logic and everything in the back-end.

Please explain me the difference with these two approaches? what why javascript frameworks play a big role? Why we need to build a web app using javascript + js frameworks? What are the advantages? disadvantages?