I'd never describe problem sets as "fun," but there's a reason teachers assign them. It's one thing to nod your head as you read a book ("yes, that makes sense") but quite another to apply what you've learned. Software is very much a "learn by doing" field. You retain knowledge better when you actively use it.
I would have liked to include exercises in Effective TypeScript but never quite got around to it. Fortunately, there are several excellent sources of TypeScript exercises and puzzles online. Here are a few:
TypeScript Exercises
I can't recommend Marat Dulin's TypeScript Exercises enough. The problems all build on one another, starting very simple and getting very complex. They have a story and a theme to them that I found thoroughly enjoyable ("CEO's friend Nick told us that if we randomly swap user names from time to time in the community, it would be very funny and the project would definitely succeed!") Marat's latest update includes a hosted version, so you can complete the exercises without leaving your browser. My solutions and commentary on a previous version are here.
Type Challenges
The Type Challenges project was created by Anthony Fu and others. (It's also available in Chinese!) These challenges are independent puzzles and can be done in any order. Each challenge takes you to a TypeScript playground with infuriating red squiggles that must be fixed. This project is very community-oriented: you're encouraged to submit your solutions and suggest other puzzles. I expect that over time it will grow to include many, many more challenges.
If you've read Effective TypeScript and want to apply what you've learned, these are both great resources. Are there others I've missed? Let me know in the comments!
