Next.js 中未定义本地存储

Question

我正在尝试将应用程序从 React 转移到 Next

在 React 中，这段代码没有错误

let [authTokens, setAuthTokens] = useState(() => localStorage.getItem('authTokens') ? JSON.parse(localStorage.getItem('authTokens')) : null)

let [user, setUser] = useState(()=> localStorage.getItem('authTokens') ? jwt_decode(localStorage.getItem('authTokens')) : null)

但是当我尝试在 Next 中使用它时，出现错误

我认为这是因为 Next 首先在服务器端呈现，而服务器端没有本地存储。

这是设置本地存储的函数。

let loginUser = async (e) => {
        e.preventDefault();
        let response = await fetch('http://127.0.0.1:8000/api/token/', {
            method:'POST',
            headers:{
                'Content-Type': 'application/json'
            },
            body:JSON.stringify({'email':e.target.username.value, 'password':e.target.password.value})
        })
        let data = await response.json()
        console.log(data)
        console.log(data.access)
        if(response.status == 200) {
            setAuthTokens(data)
            setUser(jwt_decode(data.access))
            localStorage.setItem('authTokens', JSON.stringify(data))
            router.push('/')
        } else {
            alert('something went wrong')
        }
    }

Answer 1

您可以使用此代码

if (typeof window !== "undefined") {
   if(response.status == 200) {
            setAuthTokens(data)
            setUser(jwt_decode(data.access))
            localStorage.setItem('authTokens', JSON.stringify(data))
            router.push('/')
        } else {
            alert('something went wrong')
        }
  }

Answer 2

当您的应用程序在服务器上呈现时，那里没有 browser API。您需要做的是仅当应用程序在浏览器中呈现时访问 localStorage。您可以通过等待安装组件然后访问 localStorage

function MyComponent(){
  // this runs only in the browser
  useEffect(()=>{
  // access local storage here
  },[])
}

Answer 3

我似乎已经通过将逻辑从 useState 移到 useEffect 中来修复它

而不是

let [authTokens, setAuthTokens] = useState(() => localStorage.getItem('authTokens') ? JSON.parse(localStorage.getItem('authTokens')) : null)

let [user, setUser] = useState(()=> localStorage.getItem('authTokens') ? jwt_decode(localStorage.getItem('authTokens')) : null)

我把 useEffect 里的逻辑搬过来了

let [authTokens, setAuthTokens] = useState(null)
let [user, setUser] = useState(null)

    useEffect(() => {
        
            if(localStorage.getItem('authTokens')) {
                setAuthTokens(JSON.parse(localStorage.getItem('authTokens')))
                setUser(jwt_decode(localStorage.getItem('authTokens')))
            } else {
                setAuthTokens(null)
                setUser(null)
            }

Next.js 中未定义本地存储

localstorage not defined in Next.js

local-storage

reactjs

next.js