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

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