This talk is about flow, a static type-checker for JavaScript which is developed and maintained by Facebook. We have been using flow extensively at QuizUp for half a year now and it’s been a great success in a big JS codebase.

In this talk I will answer the following questions:

• What is it?
• Why use it?
• What can it do?
• What can’t it do?

Lastly I will go over lessons learned and our experience with using flow.