June 2nd, 2021 × #react#typescript#webdev

React + TypeScript

Discussion on setting up React with TypeScript, typing components, props, state, hooks, and other common patterns when using the two technologies together.

Show Notes Transcript

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) => <div />

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 (
    <li>
        {joke.joke} = {joke.id}
    </li>
    );
}

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<User | null>(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<HTMLElement>(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<AppContextInterface | null>(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<HTMLSelectElement>) =>
    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<Ref, Props>((props, ref) => (
  <button ref={ref} className="MyClassName" type={props.type}>
    {props.children}
  </button>
));

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
}