[React Typescript 2022] Refactor a React Component using TypeScript

We are going to start refactoring our CountDisplay component. It is a small stateless component but it has a few props that can benefit from type safety.

There are three ways to type a component, inline, alias, and as a function expression. The inline typing adds a bit of noise to our code and can make it difficult to parse right out of the gate. To fix this, we use a type alias that reads a little bit nicer. To add in a function expression, which we get from the React Types that we downloaded, we can declare this variable to have a type of React.FunctionComponent which takes as a type argument, our props.

JS:

import * as React from "react";
import cx from "clsx";
import { scope } from "../lib/utils";

function CountDisplay({ count, className }) {
    let countString = String(Math.max(Math.min(count, 999), -99));
    return (
        <div className={cx(scope("count-display"), className)}>{countString}</div>
    );
}

export { CountDisplay };

TS:

import * as React from "react";
import cx from "clsx";
import { scope } from "../lib/utils";

function CountDisplay({ count, className }: CountDisplayProps) {
    let countString = String(Math.max(Math.min(count, 999), -99));
    return (
        <div className={cx(scope("count-display"), className)}>{countString}</div>
    );
}

export { CountDisplay };

interface CountDisplayProps {
    count: number;
    className?: string;
}

Or:

For function component:

TS:

import * as React from "react";
import cx from "clsx";
import { scope } from "../lib/utils";

const CountDisplay: React.FunctionComponent<CountDisplayProps> = ({
    count,
    className,
}) => {
    let countString = String(Math.max(Math.min(count, 999), -99));
    return (
        <div className={cx(scope("count-display"), className)}>{countString}</div>
    );
};

CountDisplay.displayName = "Count";

export { CountDisplay };

interface CountDisplayProps {
    count: number;
    className?: string;
}

or a Shorter way:

const CountDisplay: React.FC<CountDisplayProps> = ({
    count,
    className,
}) => {
    let countString = String(Math.max(Math.min(count, 999), -99));
    return (
        <div className={cx(scope("count-display"), className)}>{countString}</div>
    );
};

FC<> always imply children, So if your component doesn't accept Children, you can use `VFC` or `VoidFunctionComponent`.

const CountDisplay: React.VFC<CountDisplayProps> = ({
    count,
    className,
}) => {
    let countString = String(Math.max(Math.min(count, 999), -99));
    return (
        <div className={cx(scope("count-display"), className)}>{countString}</div>
    );
};

Read more 

TypeScript + React: Why I don't use React.FC