There were 3 rounds (I didn't make it beyond that; there would be 5 in general):

1. Intro round, just to verify your candidature.
2. 60 min, 1-1 pair programming round.
3. 60-90 min, 2:1 grilling interview.

Pair programming rounds are part of a complete project. This is not framework specific; ensure that you know core JavaScript in depth.

Be prepared with basic things like getting hold of elements and manipulating elements. They'll let you sneak the API, but it's better to be prepared in advance.

The tech interview is split into three parts:

Part I - Deep discussion of a project you've worked on in the past. Part II - Chat about certain topics. Part III - Another round of pair programming.

This is more of a depth test than anything. The first two parts will have a lot of counter-questions and knowledge of JavaScript.