Mastering State and Type Safety in React with TypeScript

In this episode of Syntax, Scott and Wes talk about using React with Typescript — how to set it up, components, state, props, passing data, custom hooks, and more!

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Show Notes

04:55 - Components

• Strategies
• Example:

type Props = { value: string; } const App = (props: Props) =>

• Return type? JSX.Element
• FC or FunctionComponent
• It’s discouraged for this reason: It means that all components accept children, even if they're not supposed to
• It could be useful for a return type

12:13 - Props

• Default props:

const defaultJoke: JokeProps = { joke: 'LOL JOE', id: 'YEAH', status: 200, }; function JokeItem({ joke = defaultJoke }: JokeProps): JSX.Element { return (

{joke.joke} = {joke.id}

); }

• Because props are always destructured, you often have to make a new type for your props. You can’t just type each argument by itself.

18:38 - State

• Just like Generics, State can be inferred
• If your type is simple and you’re using useState, it just works: const [user, setUser] = useState(null);

22:27 - useEffect

• Nothing special required
• Good use of void: If you want to use a Promise function but not worry about await or .then(), you can pop a void in front of it:

useEffect(() => { console.log('Mounted'); // getJoke().then(console.log).catch(console.error); void getJoke(); }, [getJoke]);

26:09 - Refs

• Very similar to state however some interesting things with null: const ref1 = useRef(null!);
• “Instantiating the ref with a current value of null but lying to TypeScript that it’s not null.”

29:33 - Custom Hooks

• This is a great use case for Tuples

31:00 - Context

• This is probably the most complex thing in this list
• First define the types
• Use generic to pass in types OR null
• This can also be non-null if you have default values in createContext: const AppCtx = React.createContext(null);

35:21 - Events

• The React events system is better than Vanilla JS
• Can handle them inline and have it inferred: onClick={e ⇒ yeah(e.target)}

const onSetType = (e: React.ChangeEvent) => setType(e.target.value)

• React has a bunch of events built in — many of them take a Generic argument so you can specify the type of element that triggered it. Handy for native API methods like play and pause.

39:27 - ForwardRef

• Again use of to pass in forwarded ref type as param 1, Props types as param 2:

type Props = { children: React.ReactNode; type: "submit" | "button" }; export type Ref = HTMLButtonElement; export const FancyButton = React.forwardRef((props, ref) => ( {props.children} ));

41:30 - ESLint

• Typescript-react is good
• Extend your own
• Most JS rules apply to TS

46:20 - React as Global React 17

• Also add JSX: True to eslint globals for typing things like JSX.Element
• global.d.ts

import * as react from "react" import * as react_dom from "react-dom" declare global { type React = typeof react type ReactDOM = typeof react_dom }

48:08 - TSConfig

• jsx: "react"
• React emit .js files with JSX changed
• Preserve .jsx file output
• React-native → .js files with jsx not changed

53:05 - Frameworks?

• Next.js makes this a TREAT
• Gatsby just use .tsx extensions
  • https://www.gatsbyjs.com/plugins/gatsby-plugin-ts-config/

Links

• https://github.com/typescript-cheatsheets/react
• Tanner Linsley
• https://github.com/wesbos/eslint-config-wesbos
• Deno
• Architect
• https://fav.farm/
• Snowpack
• Vite
• Parcel 2
• Foam

××× SIIIIICK ××× PIIIICKS ×××

• Scott: Obsidian
• Wes: Folding Allen Keys

Shameless Plugs

• Scott:
  • 1: Level Up Tutorials Pro Spring Sale - 50% off annual subscriptions!
  • 2: SvelteKit Course
• Wes: Beginner Javascript Course - Use the coupon code ‘Syntax’ for $10 off!

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