Two steps:
1 - Coding test: In this, you'll be asked to write an app from scratch according to your preference (backend or frontend). The backend app is a simple API that should implement some simple features described by a gist document. The frontend one is a consumer of the API described in the previous test. Your interviewer you'll give you an array of frameworks for you to choose from and you'll have from 3 to 5 days to send the result back.
2 - Interview: questions regarding your work background. This changes a lot from office to office.