I was referred by a friend and had an on site interview. I interviewed with the CTO of the company and he went through my resume and asked questions about my projects and previous job experiences. He then went on my github and looked at some of my codes and asked me to explain some parts of my code. It was not a very formal interview and I think what matters most is that you have some experience of programming and you can show them that you are a quick learner and have good attitude. At the end they let you know whether your a good fit for them and how the interview went and wont let you hanging for a couple of weeks.