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You need integration-level tests around every method call Sure, but you need those tests anyway to verify that your code actually works. I agree that type syst

You need integration-level tests around every method call Sure, but you need those tests anyway to verify that your code actually works. I agree that type systems reduce the occurrences of some classes of bugs; I'm only disagreeing with the claim that they reduce the amount of tests you need to write.

josephg 6y ago
I used to agree with you, and somewhere in my comment history on HN you’ll find similar comments to yours. But I think I was wrong. I recently ported some (quite complex) code I wrote from JavaScript to Typescript. The code has about a 2:1 test to code ratio, and a fuzzer for correctness. While porting, I ended up adding a couple “useless” assert(typeof x === ...) calls to quieten the compiler, which felt useless because my code was correct. Lo and behold, the assertion tripped in my test suite - apparently I was sometimes treating a string as an object and didn’t notice. Which was a serious issue; and could end up being a security problem for some people. My fuzzer didn’t find it because it never occurred to me to add string method names in my random data generator. Generally I find that the bugs that are easy to find with tests and the bugs that are easy to find with static types are different. You can eventually find all bugs with a sufficiently large test suite; and with enough PhDs you can apparently formally prove everything. But you get the best bang for buck with a little of each. A few tests is much better than no tests. But in the same spirit, I find no matter how big my test suite, there’s a good chance static types will improve my code. Typescript is far from perfect, but I sleep better at night with a type checker checking my code.
- orangecat 6y ago
  Generally I find that the bugs that are easy to find with tests and the bugs that are easy to find with static types are different. I don't think we disagree much. As your experience shows, trying to replicate type checking via unit tests is almost always impractical. Which means the tradeoff of not having static typing is not that you're writing more tests, but that there's an increased chance of bugs. And I agree that once a JS project is large enough to have a build process, the benefits of TypeScript almost always outweigh the costs. I'd even like to see JS interpreters allow and ignore TypeScript types, so you could use it without a build step.

josephg 6y ago

I used to agree with you, and somewhere in my comment history on HN you’ll find similar comments to yours. But I think I was wrong. I recently ported some (quite complex) code I wrote from JavaScript to Typescript. The code has about a 2:1 test to code ratio, and a fuzzer for correctness. While porting, I ended up adding a couple “useless” assert(typeof x === ...) calls to quieten the compiler, which felt useless because my code was correct. Lo and behold, the assertion tripped in my test suite - apparently I was sometimes treating a string as an object and didn’t notice. Which was a serious issue; and could end up being a security problem for some people. My fuzzer didn’t find it because it never occurred to me to add string method names in my random data generator. Generally I find that the bugs that are easy to find with tests and the bugs that are easy to find with static types are different. You can eventually find all bugs with a sufficiently large test suite; and with enough PhDs you can apparently formally prove everything. But you get the best bang for buck with a little of each. A few tests is much better than no tests. But in the same spirit, I find no matter how big my test suite, there’s a good chance static types will improve my code. Typescript is far from perfect, but I sleep better at night with a type checker checking my code.

orangecat 6y ago
Generally I find that the bugs that are easy to find with tests and the bugs that are easy to find with static types are different. I don't think we disagree much. As your experience shows, trying to replicate type checking via unit tests is almost always impractical. Which means the tradeoff of not having static typing is not that you're writing more tests, but that there's an increased chance of bugs. And I agree that once a JS project is large enough to have a build process, the benefits of TypeScript almost always outweigh the costs. I'd even like to see JS interpreters allow and ignore TypeScript types, so you could use it without a build step.