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Learn how to unleash the full potential of the type system of TypeScript

type-level-typescript.com

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Re: Learn how to unleash the full potential of the type system of TypeScript

#111

Post by Etheryte »

somewhereoutth wrote: post #91

> Over the years, the type system of TypeScript has grown from basic type annotations to a large and complex programming language. Give someone (particularly a developer) the opportunity to build something complicated and undoubtedly they will. So now you have two problems, the complicated program that actually does some hopefully useful work, and another complicated program on top of it that fills your head and slow…

Hard disagree. For me, the proof is in the pudding. When writing regular Javascript, I need to run and debug my code often as I'm developing it to make sure all intermediate states make sense and that there's no edge cases I've missed. With Typescript I can often write code for hours without even starting it up, and when I finally do run it, it usually works correctly right out of the box.

Re: Learn how to unleash the full potential of the type system of TypeScript

#112

Post by dragonwriter »

somewhereoutth wrote: post #91

> Over the years, the type system of TypeScript has grown from basic type annotations to a large and complex programming language. Give someone (particularly a developer) the opportunity to build something complicated and undoubtedly they will. So now you have two problems, the complicated program that actually does some hopefully useful work, and another complicated program on top of it that fills your head and slow…

> Almost all bugs are logic bugs or inconsistent state bugs (thanks OOP!), almost none are type bugs.

Most, possibly all, inconsistent state bugs and many logic bugs are type bugs with a sufficiently-expressive type system properly used. That's why type systems have progressed from basic systems evolved from ones whose main purpose was laying out memory rather than correctness to more elaborate systems.

Re: Learn how to unleash the full potential of the type system of TypeScript

#113

Post by adamddev1 »

iainmerrick wrote: post #63
323 wrote: post #37

One think I struggled a lot with until I got it is that the TypeScript types and the JavaScript code live in totally separate universes, and you cannot cross from the type world to JavaScript values because the types are erased when transpilling - meaning they can't leave any trace. This means that it's impossible to write this function: function isStringType (): boolean { return ... } const IS_STRING: boolean = isSt…

I think that’s actually a positive feature of TypeScript -- a useful limitation. Reflection is generally a bad idea and it’s good to be forced to do without it. It is a bit annoying sometimes that you can’t have overloaded functions with different types, but in that case you can usually just give the overloads different names, and usually that’s better for readability anyway. (Or if you really want to, write one func…

How do you give the overloads different names? Can you give a little example?

Re: Learn how to unleash the full potential of the type system of TypeScript

#114

Post by pragmatic »

tunesmith wrote: post #45

Might as well ask here. On our teams, we have the occasional developer that is insistent on using Typescript in an OO fashion. This has always struck me as square peg round hole. Even though I come from an OO background, Typescript strict settings really seem to push me in a direction of using interfaces and types for type signatures, and almost never classes, subclasses, instantiated objects. I don't have a very goo…

Either is valid.

If you got your first taste of typescript from angular and have a full stack background in c#/ Java class based style will make you feel right at home.

React seems to oscillate between the 2 styles.

My recent work in Svelte send to favor functions and types.

IMO the biggest benefit of classes is the code organization it brings. Have you ever seen a “util” class or folder. That’s what tends to happen to a code base without strong cohesion. It becomes hard to find anything.

With typescript/js you have modules as a pretty good substitute.

What I love about typescript is that you can mix the two.

Mostly classless module based with the occasional class (logger with a constructor to pass in the current module name for example) seems to be what I like most now. Use what makes sense.

Re: Learn how to unleash the full potential of the type system of TypeScript

#115

Post by hither_shores »

somewhereoutth wrote: post #91

> Over the years, the type system of TypeScript has grown from basic type annotations to a large and complex programming language. Give someone (particularly a developer) the opportunity to build something complicated and undoubtedly they will. So now you have two problems, the complicated program that actually does some hopefully useful work, and another complicated program on top of it that fills your head and slow…

> Almost all bugs are logic bugs or inconsistent state bugs (thanks OOP!), almost none are type bugs.

With a sufficiently powerful type system (and typescript is basically the only non-functional language that makes the cut here) these aren't all that distinct. But even in codebases that don't take advantage of that power, this has not been my experience. I recently converted about ten thousand lines of legacy javascript to typescript at work, and discovered several hundred type errors in the process. State bugs also slip through pretty often, but we almost always catch pure business logic errors at code review.

Re: Learn how to unleash the full potential of the type system of TypeScript

#116

Post by [deleted] »

cogman10 wrote: post #86
marcosdumay wrote: post #32

Earlier quoted context omitted.

The types in your code are just as designed just like any other aspect of it. It's not a matter of restraint, it's a matter of doing things on the correct way.

I don't believe in "correct" when it comes to software dev. There's 1000 solutions to any given problem. It's a matter of choosing a solution that is clear, easy to understand, and easy to maintain. There are nearly limitless solutions that can fit that definition. Restraint comes into play because devs tend to "treat every problem like a nail when they have a hammer". When devs learn new concepts, they often look fo…

[deleted]

Re: Learn how to unleash the full potential of the type system of TypeScript

#117

Post by robertwt7 »

Really interesting articles, will definitely have a look at night.

After so many years of JS programming, moving to a company that uses TS extensively (in a huge scale) feels life changing. You don't even know the effect until you use it daily. Even so, daily usage of typescript at a large web application doesn't seem to be using its full potential. I feel like libraries creator and maintainer use them more in the definitions that they created (i.e redux toolkit type is mind blowing).

Thanks for creating this lesson, it will definitely teach me a lot

Re: Learn how to unleash the full potential of the type system of TypeScript

#118

Post by Aeolun »

Etheryte wrote: post #111
somewhereoutth wrote: post #91

> Over the years, the type system of TypeScript has grown from basic type annotations to a large and complex programming language. Give someone (particularly a developer) the opportunity to build something complicated and undoubtedly they will. So now you have two problems, the complicated program that actually does some hopefully useful work, and another complicated program on top of it that fills your head and slow…

Hard disagree. For me, the proof is in the pudding. When writing regular Javascript, I need to run and debug my code often as I'm developing it to make sure all intermediate states make sense and that there's no edge cases I've missed. With Typescript I can often write code for hours without even starting it up, and when I finally do run it, it usually works correctly right out of the box.

It’s certainly nice that you know your code will still run when any of your values are null or undefined, and you are forced to deal with that scenario.

Re: Learn how to unleash the full potential of the type system of TypeScript

#119

Post by hither_shores »

323 wrote: post #50
agentultra wrote: post #17

Nice course, and nice site. Although, as a Haskell developer, I am curious what type system TS is using (System F? Intuitionist? etc) and what limitations one can expect. Aside from the syntax of TS being what it is, what are the trade-offs and limitations? I was under the impression, and this was years ago -- things are probably different now?, that TS's type system wasn't sound (in the mathematical logic sense).

Non-soundness is sort of a feature, it lets you force your way through and just say "trust me, this is a Thing" when it's just hard (or impossible) to make TypeScript see that. In practice, you can write large code bases where you only need to do this every 1000 lines or so. Not ideal, but better than no typing.

Being able to opt in to unsoundness is arguably a feature, but TypeScript is still unsound even without using assertions or `any`.

Re: Learn how to unleash the full potential of the type system of TypeScript

#120

Post by Aeolun »

somewhereoutth wrote: post #107
edgyquant wrote: post #92

Earlier quoted context omitted.

Have you worked with typescript? Adding strict types to JavaScript fixes pretty much all the complaints I use to have when working with frontend services/clients. Typescript isn’t a “now you have two problems” anymore than types in any other language are.

Maybe in a controlled environment Typescript can produce benefits - however much of my argument is that our environments are typical uncontrolled , let's not give the monsters any more magic than we have to.

I’m inclined to say that any magic applied here is a win. Making things complicated with Typescript is simply hard enough that those people that’d mess things up in the first place wouldn’t even consider trying.
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