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I still don't see the value added by TypeScript. My JavaScript tests catch typoed property names every time. I can't remember the last time I merged code with a

I still don't see the value added by TypeScript. My JavaScript tests catch typoed property names every time. I can't remember the last time I merged code with a typo in a property name. IMO, if you typoed a property name and your tests didn't catch it, it means that either your tests are poorly written or your object didn't need that property to begin with.

nicoburns 7y ago
Type systems can be thought of as low-cost (in terms of dev time) declarative tests. Which should leave you with less to test in your actual tests. They also give much quicker feedback than tests.
- cryptica 7y ago
  Is TypeScript low-cost? Most TS projects I've worked on had at least a 10 to 30 seconds build waiting time per iteration. This means that every time I make a change and run the tests, I need to wait 10 to 30 seconds. With my iterative test-driven approach, I probably iterate about once every minute on average (also, my development iteration time gets faster as I become more experienced in the project). So 30 seconds represents 50% of my total development time. Meaning that I could have written 50% more tests or 50% more features in the same amount of time. And that's not even accounting for my loss of focus incurred as a result of waiting 30 seconds to see the result of my code change. By the time I see the result, the concept in my mind is not as fresh as it was 30 seconds earlier.
  - Fannon 7y ago
    Are you aware of tsc options like --watch and --incremental ? Combined with other live-reloading tools like nodemon or jest --watch you can have almost the same speed of your development-test-run-debug loops as in plain JS. But you do gain an additional instant feedback channel from the compiler.
- kjtekn 7y ago
  No longer enjoying programming is a cost nobody can afford to pay. When I read the long list of c#, I mean typescript documentation, it gives me PTSD from c# and java, which people used to hate here, but now suddenly like and let me tell you it has nothing to do with microsoft social engineering.
  - BorisTheBrave 7y ago
    Devs should enjoy writing trivial tests? Heaven forbid businesses might care how quickly something is delivered? Let us know when you are willing join the rest of us in the real world.
  - TomMarius 7y ago
    I also used to think TS is like C#. Huge mistake. Try to approach it from a functional angle. The TS compiler code does not use the class keyword.
DonHopkins 7y ago
Do your JavaScript tests inform your IDE how to do code highlighting and completion and refactoring?
- cryptica 7y ago
  My JavaScript integration and unit tests do something better; they tell me exactly what features I broke as a result of my refactoring and let me fix things in the best way possible without regard for the previous structure of the code (which may no longer be relevant anyway; there is usually a good reason why we do refactorings in the first place! It's rarely just about renaming things). I have many stories on the subject but most recently I did a significant refactoring for a JavaScript project (a popular open source library I created) to move from callbacks to async/await and was able to re-use pretty much all of the existing integration test logic with only aesthetic changes (to account for the new async/await API). When I finished the refactoring, I had modified at least 70% of the entire source code of the project and I took it as an opportunity to make significant structural changes to my code to align with the new async/await flow in the most optimal way possible. This kind of big refactoring would have made code highlighting completely redundant and would have prevented me from looking at the problem with a fresh mind and taking into account the new features offered by async/await. It was a very successful refactoring; no new issues were uncovered after the point that I managed to get all the original tests passing again and the code was a lot simpler than before. I think TS has a way of locking down old structures in a way that make it sub-optimal in the long run. Feature-oriented tests are by far the best way to ensure that product quality is maintained after a refactoring IMO.
  - the_gipsy 7y ago
    I have the exact opposite opinion on "code lockdown". I believe that unit and integration tests heavily lock down code, so much as being mere checksums. In a project with >90% coverage, I would find refactors dreadful. After any substantial change beyond adding stuff, there were always a myriad of tests failing. Not hard to fix, but simply tedious and dreadful. On the other hand, I have an Elm project with no unit test, only some e2e tests. I can do huge transversal changes, and I don't find ot tedious at all. It gave me back the fun in programming. The Elm project is a game, so there should me an order of magnitude more bugs, but the opposite was the case.
redmorphium 7y ago
Some Typescript value added: - Living documentation: types are a clear description of how your code and its data are laid out, and this structure is kept always up-to-date with the code, regardless of future changes. If the "documentation" (the typing) is wrong, the compiler will complain. - Better tooling: autocomplete, more robust auto-refactoring - Elimination of an entire class of bugs. This class may include: 1. `Cannot read property 'foo' of undefined` 2. forgeting a case in a switch statement 3. `'foo' is not a function` 4. in general, your code receiving data that isn't laid out in a way you expected (Property typos is one within this class of bugs, but it is not all of it) Yes tests catch these bugs as well. But tests are also manually written. And often not written at all. A compiler makes these (mundane) sanity checks automatic and mandatory. --- Typescript's slogan is "JavaScript that scales" because static typing improves: dev documentation (via types living inside the code) and dev tooling (refactoring and autocomplete), both of which help immensely as a project grows in age (devs become forgetful), team size (new developers get lost), and convolutedness (e.g. tech debt).
- kjtekn 7y ago
  Lets be honest here, these reasons are really weak. Living documentation - TypeScript is less readable. There is more stuff you have to read. Stuff that isn't even relevant. I see a "cars" variable. Oh no, I don't know what type it is, I am going to have a panic attack. Don't worry that cars.map((c) => c.model); is the next line or whatever. What type is it, I must know! auto-refactoring.. yeah we all trust that. Until you come to the boundaries where all the types don't exist, like from the client to the server, to the database via its message system, etc. All the stuff coming in and out of your code is untyped. Autocomplete works without typescript, even if it uses "the typescript engine". The types aren't needed. Eliminates an entire class of bugs that nobody has ever had a problem with.
  - eatonphil 7y ago
    > All the stuff coming in and out of your code is untyped. Until you automate building TypeScript definitions from your external code. We do this to varying degrees and are always trying to improve.
lscharen 7y ago
If TypeScript is used against bog-standard JS code, I can definitely appreciate your point. For me, TypeScript really started to shine once I started taking advantage its generic support, higher-level utility types like Pick<> and Optional<> (and really anything involving keyof), and creating static type checks via the unknown and never types. This is especially effective when working on legacy JS code bases where unit tests and other good engineering principles were not used well, or at all.
vhakulinen 7y ago
> My JavaScript tests catch typoed property names every time. My typescript compiler catches typoed property names every time. > I can't remember the last time I merged code with a typo in a property name. I can't remember the last time my newly written code made it into the runtime/browser with a typo in a property name. > ...if you typoed a property name and your tests didn't catch it, it means that either your tests are poorly written or your object didn't need that property to begin with. The types are much more than just property names.

nicoburns 7y ago

Type systems can be thought of as low-cost (in terms of dev time) declarative tests. Which should leave you with less to test in your actual tests. They also give much quicker feedback than tests.

cryptica 7y ago
Is TypeScript low-cost? Most TS projects I've worked on had at least a 10 to 30 seconds build waiting time per iteration. This means that every time I make a change and run the tests, I need to wait 10 to 30 seconds. With my iterative test-driven approach, I probably iterate about once every minute on average (also, my development iteration time gets faster as I become more experienced in the project). So 30 seconds represents 50% of my total development time. Meaning that I could have written 50% more tests or 50% more features in the same amount of time. And that's not even accounting for my loss of focus incurred as a result of waiting 30 seconds to see the result of my code change. By the time I see the result, the concept in my mind is not as fresh as it was 30 seconds earlier.
- Fannon 7y ago
  Are you aware of tsc options like --watch and --incremental ? Combined with other live-reloading tools like nodemon or jest --watch you can have almost the same speed of your development-test-run-debug loops as in plain JS. But you do gain an additional instant feedback channel from the compiler.
kjtekn 7y ago
No longer enjoying programming is a cost nobody can afford to pay. When I read the long list of c#, I mean typescript documentation, it gives me PTSD from c# and java, which people used to hate here, but now suddenly like and let me tell you it has nothing to do with microsoft social engineering.
- BorisTheBrave 7y ago
  Devs should enjoy writing trivial tests? Heaven forbid businesses might care how quickly something is delivered? Let us know when you are willing join the rest of us in the real world.
- TomMarius 7y ago
  I also used to think TS is like C#. Huge mistake. Try to approach it from a functional angle. The TS compiler code does not use the class keyword.

DonHopkins 7y ago

Do your JavaScript tests inform your IDE how to do code highlighting and completion and refactoring?

cryptica 7y ago
My JavaScript integration and unit tests do something better; they tell me exactly what features I broke as a result of my refactoring and let me fix things in the best way possible without regard for the previous structure of the code (which may no longer be relevant anyway; there is usually a good reason why we do refactorings in the first place! It's rarely just about renaming things). I have many stories on the subject but most recently I did a significant refactoring for a JavaScript project (a popular open source library I created) to move from callbacks to async/await and was able to re-use pretty much all of the existing integration test logic with only aesthetic changes (to account for the new async/await API). When I finished the refactoring, I had modified at least 70% of the entire source code of the project and I took it as an opportunity to make significant structural changes to my code to align with the new async/await flow in the most optimal way possible. This kind of big refactoring would have made code highlighting completely redundant and would have prevented me from looking at the problem with a fresh mind and taking into account the new features offered by async/await. It was a very successful refactoring; no new issues were uncovered after the point that I managed to get all the original tests passing again and the code was a lot simpler than before. I think TS has a way of locking down old structures in a way that make it sub-optimal in the long run. Feature-oriented tests are by far the best way to ensure that product quality is maintained after a refactoring IMO.
- the_gipsy 7y ago
  I have the exact opposite opinion on "code lockdown". I believe that unit and integration tests heavily lock down code, so much as being mere checksums. In a project with >90% coverage, I would find refactors dreadful. After any substantial change beyond adding stuff, there were always a myriad of tests failing. Not hard to fix, but simply tedious and dreadful. On the other hand, I have an Elm project with no unit test, only some e2e tests. I can do huge transversal changes, and I don't find ot tedious at all. It gave me back the fun in programming. The Elm project is a game, so there should me an order of magnitude more bugs, but the opposite was the case.

redmorphium 7y ago

Some Typescript value added: - Living documentation: types are a clear description of how your code and its data are laid out, and this structure is kept always up-to-date with the code, regardless of future changes. If the "documentation" (the typing) is wrong, the compiler will complain. - Better tooling: autocomplete, more robust auto-refactoring - Elimination of an entire class of bugs. This class may include: 1. `Cannot read property 'foo' of undefined` 2. forgeting a case in a switch statement 3. `'foo' is not a function` 4. in general, your code receiving data that isn't laid out in a way you expected (Property typos is one within this class of bugs, but it is not all of it) Yes tests catch these bugs as well. But tests are also manually written. And often not written at all. A compiler makes these (mundane) sanity checks automatic and mandatory. --- Typescript's slogan is "JavaScript that scales" because static typing improves: dev documentation (via types living inside the code) and dev tooling (refactoring and autocomplete), both of which help immensely as a project grows in age (devs become forgetful), team size (new developers get lost), and convolutedness (e.g. tech debt).

kjtekn 7y ago
Lets be honest here, these reasons are really weak. Living documentation - TypeScript is less readable. There is more stuff you have to read. Stuff that isn't even relevant. I see a "cars" variable. Oh no, I don't know what type it is, I am going to have a panic attack. Don't worry that cars.map((c) => c.model); is the next line or whatever. What type is it, I must know! auto-refactoring.. yeah we all trust that. Until you come to the boundaries where all the types don't exist, like from the client to the server, to the database via its message system, etc. All the stuff coming in and out of your code is untyped. Autocomplete works without typescript, even if it uses "the typescript engine". The types aren't needed. Eliminates an entire class of bugs that nobody has ever had a problem with.
- eatonphil 7y ago
  > All the stuff coming in and out of your code is untyped. Until you automate building TypeScript definitions from your external code. We do this to varying degrees and are always trying to improve.

lscharen 7y ago

If TypeScript is used against bog-standard JS code, I can definitely appreciate your point. For me, TypeScript really started to shine once I started taking advantage its generic support, higher-level utility types like Pick<> and Optional<> (and really anything involving keyof), and creating static type checks via the unknown and never types. This is especially effective when working on legacy JS code bases where unit tests and other good engineering principles were not used well, or at all.

vhakulinen 7y ago

> My JavaScript tests catch typoed property names every time. My typescript compiler catches typoed property names every time. > I can't remember the last time I merged code with a typo in a property name. I can't remember the last time my newly written code made it into the runtime/browser with a typo in a property name. > ...if you typoed a property name and your tests didn't catch it, it means that either your tests are poorly written or your object didn't need that property to begin with. The types are much more than just property names.