18. How would you create google analytics script.

You should get yourself familiar with Google Analytics, or even better if you can try it out in your own websites.

Oversimplified, Google Analytics allows us to track client-side events with easy-to-integrate script tag and then do complex analysis with their dashboard.

For example, you can cover topics like:

1. script tag API design
2. loading strategy
3. performance concerns
4. reliability
5. cache control and update strategy
6. data protocol
7. some basic backend design including load balancing and storage .etc