[React] State and Callbacks Don’t Mix Well in React

// Doesn't work

import React from 'react'
import { saveInfo } from './api'

export default function App() {
    const [count, setCount] = React.useState(0)
    
    async function onClick() {
        // because this is async api call
        // react will wait until this api resolve
        // during the waiting time, react component won't rerender
        // therefore count will be 1
        await saveInfo()
        setCount(count + 1)
    }
    
    return (
        <>
         <h1>Count: {count}</h1>
         <button onClick={onClick}>+1</button>
        </>
    )
}

Solution:

import React from 'react'
import { saveInfo } from './api'

export default function App() {
    const [count, setCount] = React.useState(0)
    
    async function onClick() {
        await saveInfo()
        setCount(count => count + 1)
    }
    
    return (
        <>
         <h1>Count: {count}</h1>
         <button onClick={onClick}>+1</button>
        </>
    )
}

Even better:

import React from 'react'
import { saveInfo } from './api'

export default function App() {
    const [count, setCount] = React.useState(0)
    const inc = () => setCount(count => count + 1)
    
    async function onClick() {
        await saveInfo()
        inc()
    }
    
    return (
        <>
         <h1>Count: {count}</h1>
         <button onClick={onClick}>+1</button>
        </>
    )
}