Just to be clear, I’m not advocating TypeScript. I’m not trying to convince everybody that TypeScript is top-notch language everyone should use. I know about its weak points and design decisions.

All I’m saying is that it is the brave new world we are living in right now, where TypeScript is one of the most used languages in our job. Since we work with TypeScript, no matter the wish, it is great to improve your skill set in it.

Each time someone sets @ts-ignore directive, sets any type or worse, have them implicitly, this “someone” ignores the type system. One of the reasoning is “I don’t like the TypeScript”, but it does not sound like an argument for me.

So that, since we already work with TypeScript, let us get ourselves familiar with what TypeScript can do, instead of ignoring it and worsening your colleagues’ lives who cares about it and the code they write!

What problem do I see nowadays

I already made a TL;DR version above, but now I can add more details to what I mean.

Most developers I work or talk with currently have a false feeling that TypeScript is not expressive enough in the type system. They used to think that TypeScript is all about “here is a string, there is a number and some object with known fields” and that’s it. But I strongly disagree with them!

TypeScript has generics, strict mode for enforcing program correctness, union and intersection types, literal types, type narrowing, conditional types and a lot more.

Sure, there is a truth in their words when we compare TypeScript type system with, e.g., Haskell type system. But, do not forget, we are talking about the language which target is JavaScript! How do you even compare those?

We got off the track, let’s get back to it. So what is the problem in my humble opinion? Personally, I think that the most issues coming from TypeScript code goes from the fact that most TypeScript developers don’t know how to express “something” in type system.

They try to write the safe code and then they get the compiler error which says something terrible happened. Especially, knowing the TypeScript has the worst error reporting and it is not user friendly, it’s not helping. Not knowing what to do, they have no choices than to leave a @ts-ignore or any and hope that someone else would come up and fix it.

Most of the time, it’s not, no one will come. And the code like this continues to grow until there is no difference between TypeScript and JavaScript, roughly saying.

How does it reflect those who write the code in strict mode

I’ve already talked about it before, but I’ll make a short thesis here once again. The entire infrastructure around TypeScript is not in a strict mode by default. You have no program correctness checks, no policies from the compiler to enforce “type coverage”. You can write code, not knowing that all the code you have is implicitly typed as any type.

In case you don’t know how to set up the “strict” mode I’m referring to, I talked about it here.

That’s the reason most of the code I see is just a JavaScript code with type hints and no policies. People just write JavaScript, sometimes leaving type hints and TypeScript strips the type when compiling - that’s it - nothing useful.

You write JavaScript, not TypeScript. The fact you use TypeScript compiler does not mean you write TypeScript code.

Don’t get me wrong, I’m not saying that you [reader] has this setup. I’m saying that there is a chance, that you have a default setup that enforces nothing. So that, you write JavaScript code, actually.

The ones who work in such a setup (the one that is default and out of the box) get used to it pretty fast. Of course, by default, TypeScript asks nothing from you, so you continue writing JavaScript, thinking you write TypeScript.

But, I’ll tell you what. There are teams that spent some time and investigated how TypeScript and ESLint can be tuned to enforce program correctness checks. These teams have strict mode set up on their projects and once they get a developer who previously worked in a non-strict mode - boom! Turns out, the developer knows nothing about TypeScript and its type system. The whole life is a lie!

Having a developer that got used to the non-strict mode is tough. In the worst-case scenarios, you get a developer that does not understand why is it everything so strict, does not see any sense in it and involves himself in a conflict with the team. I’ll not be talking about how much conflicts cost, that’s another topic.

Pretty soon, the developer understands that the compiler errors he sees can (and must) be fixed somehow, but how? Well, by learning the type system!

You can change it

The good point here is that you can change it! The TypeScript type system is not so expressive and hard to understand comparing with Haskell type system. Or, comparing with Rust, you don’t need to understand the ownership memory model to write types in TypeScript.

TypeScript type system is a good balanced type system. It is flexible enough to skip some type errors and leave it for later until you figure out how to fix it. On the other hand, it can provide an adequate program correctness checks (it’s not Rust, sorry, but that’s the cost of flexibility).

I would say that TypeScript is a good entry point to learn type systems. But, be aware, each language has different type systems and you need to adapt to each one of them.

Anyway, where from should you begin if you are interested in improving your skill set?

TypeScript Handbook

TypeScript team has its own handbook where all the required knowledge about type system stored. You can find there a lot of information on generics, how do they work, how implicit inferring works and so on and so forth.

Moreover, TypeScript team published its second revision recently with a lot of info structured in a more intuitive way. So before talking about improving our skill sets, you must read the handbook from A to Z, no excuses.

Type Challenges

Once you get yourself familiar with what TypeScript can do, you need to test it somewhere. Unfortunately, not everyone has projects where all this knowledge can be applied. Some projects are too easy from technical perspective so that their glass ceiling is using generic types and sometimes inferring. In such case, you can refer to Type Challenges!

Type Challenges is a project where many many challenges aggregated in one repository. The key point in these challenges is that to solve them you need to write the code in a type system. No runtime, no tests, just types! These types must solve the challenge starting from picking the property from literal type to implementing a parser for JSON on type level.

Every challenge from there is beautiful on its own. But, what to do if you tried to solve it and couldn’t?

Solutions for Type Challenges

When talking about challenges, there are two categories of solutions: bare minimum or pretty explained.

Bare minimum provides a code you need to get stuff working with no explanation at all. So, in case you couldn’t solve a challenge yourself, you can find a quick solution and pass it. But, there is a chance that you will not understand what is going on with the solution. Yes, you get the solution working, but you don’t understand why.

That’s when pretty explained solutions are coming into the game. These explanations do not just share the solution you need. They also provide a step-by-step explanation. How did we come up with the code? Why using this technique and not the other? Where can I read more about it? And many more questions like these.

If you are a fan of such explanations and challenges, you can go to Type Challenges Solutions project and find pretty explained solutions for Type Challenges there.

Epilogue

What I was trying to say with all this stuff written above? Well, I built the plan of this post around the idea that people usually do “not great” things not because they are want to do them, but because they don’t know how to do better.

I projected this idea to the TypeScript and its type system. And I thought, many TypeScript developers write “not great” code not because this is their deliberate choice, but because they don’t know how to express what they want.

So that, I told you about TypeScript Handbook, Type Challenges project where you can experiment with the challenges. Also, told you about the project that provides pretty explained solutions for those challenges.

I really believe that having all these amazing projects we can improve our skill sets when writing TypeScript code!


Eugene Obrezkov, Software Engineer at Wix.com, Kyiv, Ukraine.

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