TypeScript Reading

Ten annotated source files cover JavaScript runtime behavior, TypeScript’s type system, and the seam between them. For every unfamiliar line, name the construct and answer:

1. What does the text parse as?
2. What exists at runtime after TypeScript erases its types?
3. What does the checker believe, and why?

Mark unexplained lines // ?. Run code only to settle disagreement.

Chapters

1. Bindings, operators, control flow
2. Functions and this
3. Objects and prototypes
4. Classes
5. Iteration and collections
6. Promises and async
7. Errors, regex, builtins
8. The type layer
9. Advanced types
10. Modules and the seam