Types Beyond TypeScript

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Everybody seems to be talking about "types" these days. From the TypeScript language to type description utilities such as prop-types and Zod, developers expect clear descriptions of the shapes of their React components, data, and hooks. Let's talk about the mindset shift that's happened over the last decade, and where types are taking us over the next one.

Brief foundations: what is TypeScript, what "type safety" means, and setting up TypeScript in a React (Next.js) projectA history of how type safety has worked in React, starting with class components

Thinking in Type(s|Script): How modeling value shapes helps raise predictability and understandability, especially in the wildest and wackiest of React architectures.

TypeScript's Limitations: By design, TypeScript can only act as a development-time type system and enforce what that system can represent. We'll want to go over what can't and/or shouldn't be represented in that type system.

Raising the Runtime: Moving those type thoughts into your React runtime with programmatic frameworks or libraries such as tRPC and Zod - especially as they integrate with React metaframeworks like Next.js and Remix.

React Specifics: How this "types-first" theory works helps improve common parts of projects in the React ecosystem: from prop-types back in the day to REST or RPC endpoints, testing, and documentation today.

ESLint lint rules to catch common async and React code bugs - and why the language is designed to let you do those dangerous things in the first place.

Ecosystem future: where the TC39 types-as-comments proposal will -and won't- take types at a language-level for JavaScript in general and React apps specifically.

By allowing our types to be a reflection of the runtime reality, we embrace types-first thinking in designing code - making our code more clear to read and update. These better-define boundaries help in everything from better-defined React component boundaries to auto-generated client<>server API bridges. Hooray, types!

Josh Goldberg
Josh Goldberg
31 min
14 Jun, 2024

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Video Summary and Transcription

This Talk explores the concept of types and their significance in software development, particularly in relation to TypeScript. It discusses the limitations and advantages of TypeScript compared to other tools like Flow and Ezno. The Talk emphasizes the role of types in bridging system boundaries and improving code quality. It also highlights the importance of type-checked linting and the future of ESLint. Additionally, the Talk mentions the benefits of faster and easier linting with projects like Biome and OXC, and recommends books for further learning.

Available in Español: Tipos más allá de TypeScript

1. Introduction to Types and TypeScript

Short description:

I'm Josh. I'm really excited to talk to you today about Types beyond TypeScript. We're going to talk about four sections. What are types? What is this whole thing? Just in case you haven't played with TypeScript or Flow yet. Second, I want to quickly cover what types aren't. I also really want to talk about the stuff types are surprisingly good at. First, what can inform types? Like how you can set up your code to be well-typed. And then lastly, what types can inform? How having well-typed code can help tools run better on your code.

Hey, everyone! Oh, sweet Jesus. That's not good. I'm Josh. I'm really excited to talk to you today about Types beyond TypeScript. Yes. As Phil said, I do open source. Feel free to talk to me after this whole thing about that. It's a wonderful world. The ecosystem is always getting better. I work on projects. Who here uses TypeScript ESLint? Yes. Who here uses ESLint in general? Yes. Who here has sworn at ESLint or TypeScript ESLint? Yes. Who here still uses Mocha? Okay. Cool. I'm not talking about Mocha today. I'm talking about Type stuff. We're going to talk about four sections. What are types? What is this whole thing? Just in case you haven't played with TypeScript or Flow yet. Second, I want to quickly cover what types aren't. Whenever there's a new tool, as you may have seen in other recent developments in life, people get really excited and they use it for things that may or may not be good fits. And they can sometimes give the tool a bad name. I also really want to talk about the stuff types are surprisingly good at. First, what can inform types? Like how you can set up your code to be well-typed. And then lastly, what types can inform? How having well-typed code can help tools run better on your code. Really cool stuff. Are we ready for all that? Yes! Friday late afternoon at a conference.

2. Types and TypeScript in JavaScript

Short description:

What are types? In order to answer that question, we have to ask, what is TypeScript? JavaScript is a syntax along with a vague specification on how to execute this syntax. The problem with this, though, is that there's no built-in way in JavaScript to declare the intent behind those values. Which is why we have TypeScript. TypeScript adds in a syntax on top of JavaScript. It's a superset, meaning it's all of JavaScript plus this new stuff, and that syntax allows us to say explicitly not just what the values are, but the intent behind those values. It's so useful that it begs the question, why don't we have other TypeScripts? There are three examples of tools that are in the same space as TypeScript but aren't as popular as it, and I want to quickly go over. First, just curious, who here used Flow at any point in time? Flow is a lot like TypeScript. It's from Facebook, but it's actually gone a different direction from TypeScript. It's still under active development. But instead of getting a lot of usage and going worldwide and making it so everyone should ever, who has ever wanted to use types could use it, Flow is a little more targeted.

What are types? In order to answer that question, we have to ask, what is TypeScript? In order to answer that question, we have to ask, what is JavaScript? What is JavaScript? At its core, JavaScript is this. JavaScript is a syntax along with a vague specification on how to execute this syntax. This is lovely. Look at this. We have a let thingy. We didn't used to have let. Used to have var. We have the ability to assign a variable to different values. The problem with this, though, is that there's no built-in way in JavaScript to declare the intent behind those values. The intent behind those values. There's no little thing you can put there to say this is only ever going to be, say, a string. And that's problematic because code gets really hard to work with at scale. Once you pass five developers, 50 developers, 500 developers, it gets really hard to manage that stuff. Which is why we have TypeScript.

TypeScript adds in a syntax on top of JavaScript. It's a superset, meaning it's all of JavaScript plus this new stuff, and that syntax allows us to say explicitly not just what the values are, but the intent behind those values. In this case, string. Now, because we have the TypeScript syntax, we can do things like the TypeScript type checker. Fun fact, written in TypeScript, and that's a CLI or API you can call to get little complaints saying, hey, you said this was going to be a string, but you gave it a number, you silly goose. That's not allowed. You can run the type checker through the language services for TypeScript, such as VS code, great editors, and those will give you the same complaints but in little red squiggly line form, type number not assignable to string. And that's really useful. It's so useful that it begs the question, why don't we have other TypeScripts? Why is TypeScript the only tool that seems to be in popular usage today for enforcing types in JavaScript code? Not that I said popular. There are other tools, but TypeScript has the mind share. Now there are three examples of tools that are in the same space as TypeScript but aren't as popular as it, and I want to quickly go over. First, just curious, who here used Flow at any point in time? A good chunk of us. Flow is a lot like TypeScript. It's from Facebook, but it's actually gone a different direction from TypeScript. It's still under active development. But instead of getting a lot of usage and going worldwide and making it so everyone should ever, who has ever wanted to use types could use it, Flow is a little more targeted.

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