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Episode 9 of 16 · Web development, end to end

TypeScript: types as a proof about a program you already wrote

Chapters

1. The proofreader and the printed book0:00
2. Everything the compiler deletes0:16
3. A claim, not a guard0:37
4. Checking is a separate job0:53
5. Strict is the whole product1:10
6. What types cost and what they buy1:27
7. A lock that measures the key1:44
8. Shape, not name2:00
9. The freshness check on a literal2:15
10. Interface or type alias2:32
11. When you actually want a name2:51
12. Functions have shapes3:08
13. The mixed drawer3:26
14. A union is an or3:42
15. The checker walks your branches3:57
16. Two narrowings that lie4:16
17. Give the union a tag4:32
18. Never, and the case you forgot4:49
19. A crate that remembers its contents5:06
20. Any forgets, a parameter remembers5:23
21. Inference writes it5:40
22. The constraint that makes it useful5:57
23. Keyof, and a key that fits6:14
24. The generic you should not write6:31
25. The ladder off the roof6:48
26. Unknown is any with a seatbelt7:03
27. Any is contagious7:19
28. A guard does the check7:36
29. As is a note to the compiler7:53
30. Satisfies, and any written down8:11
31. The customs desk8:28
32. The cast that ships8:47
33. Parse, do not assert9:06
34. One schema, both sides9:23
35. Where the boundaries actually are9:41
36. A proof about the program you already wrote10:01
37. The whole thing10:17

TypeScript: types as a proof about a program you already wrote. A proofreader marks up a manuscript in red. The printed book carries none of those marks. TypeScript is that proofreader. It reads your JavaScript, argues with you about it, and th

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