Javascript 刷新页面时,上下文状态未定义
我正在创建一个社交媒体应用程序,当我与用户登录时,我会将令牌保存在本地存储中,并将用户信息放入上下文中,以便在几个组件中使用它,然后它会工作,但当我刷新页面时,数据会消失,上下文未定义。我做错了什么 我的App.jsJavascript 刷新页面时,上下文状态未定义,javascript,reactjs,react-hooks,use-context,Javascript,Reactjs,React Hooks,Use Context,我正在创建一个社交媒体应用程序,当我与用户登录时,我会将令牌保存在本地存储中,并将用户信息放入上下文中,以便在几个组件中使用它,然后它会工作,但当我刷新页面时,数据会消失,上下文未定义。我做错了什么 我的App.js function App() { const [userData, setUserData] = useState({ name: "", lastname: "", username: "
function App() {
const [userData, setUserData] = useState({
name: "",
lastname: "",
username: "",
email: "",
});
return (
<Router>
<userContext.Provider value={{ userData, setUserData }}>
<div className="app">
<Switch>
<Route exact path="/" component={Login} />
<Route path="/register" component={Register} />
<Route path="/home" component={Home} />
<Route path="/profile" component={Profile} />
</Switch>
</div>
</userContext.Provider>
</Router>
);
}
函数应用程序(){
const[userData,setUserData]=useState({
姓名:“,
姓氏:“,
用户名:“”,
电邮:“,
});
返回(
);
}
我的Login.js
function Login() {
const history = useHistory()
const {userData, setUserData} = useContext(userContext)
const [loginUser, setLoginUser] = useState({
email: '',
password: ''
})
const [error, setError] = useState()
const {email, password} = loginUser
const handleOnChange = (e) => {
setLoginUser({ ...loginUser, [e.target.name]: e.target.value})
}
const handleOnSubmit = (e) => {
e.preventDefault()
axios.post("http://localhost:5000/login", loginUser)
.then((res) => {
setUserData({
name: res.data.user.name,
lastname: res.data.user.lastname,
username: res.data.user.username,
email: res.data.user.email,
})
localStorage.setItem("auth-token", res.data.token)
history.push("/home")
})
.catch(err => {
err.response.data.msg && setError(err.response.data.msg)
})
}
return (
<div className="login">
<div>
<form onSubmit={handleOnSubmit} className="login-form">
{error ? <h4 className='login-error'>{error}</h4> : ""}
<input type="email" placeholder="Email or username" value={email} name='email' onChange={e => handleOnChange(e)}/>
<input type="password" placeholder="Password" value={password} name='password' onChange={e => handleOnChange(e)}/>
<Button type="submit" variant="contained">Log in</Button>
<div></div>
<p>Don't have an account? <Link to="/register">Click here</Link></p>
</form>
<h1>Raise your word <TwitterIcon className="login-right-icon"/></h1>
</div>
</div>
)
}
函数登录(){
const history=useHistory()
const{userData,setUserData}=useContext(userContext)
常量[loginUser,setLoginUser]=useState({
电子邮件:“”,
密码:“”
})
const[error,setError]=useState()
const{email,password}=login用户
常数变化=(e)=>{
setLoginUser({…loginUser[e.target.name]:e.target.value})
}
const handleOnSubmit=(e)=>{
e、 预防默认值()
axios.post(“http://localhost:5000/login“,登录用户)
。然后((res)=>{
setUserData({
名称:res.data.user.name,
lastname:res.data.user.lastname,
用户名:res.data.user.username,
电子邮件:res.data.user.email,
})
setItem(“auth token”,res.data.token)
历史记录。推送(“/主页”)
})
.catch(错误=>{
err.response.data.msg&&setError(err.response.data.msg)
})
}
返回(
{错误?{error}:“}”
更改(e)}/>
更改(e)}/>
登录
没有帐户?请单击此处
说话算数
)
}
My Home.js,如果刷新,则会丢失上下文中的数据
function Home() {
const {userData, setUserData} = useContext(userContext)
const [posts, setPost] = useState([])
const [createPost, setCreatePost] = useState('')
const handleToken = () => {
localStorage.removeItem('auth-token')
}
const token = localStorage.getItem("auth-token");
const handleOnSubmit = (e) => {
e.preventDefault()
axios.post('http://localhost:5000/posts', {textOfThePost: createPost}, {
headers: { 'auth-token': token },
})
.then((res) => {setCreatePost("")})
}
useEffect(() => {
axios.get('http://localhost:5000/posts')
.then(res => {
setPost(res.data)
})
}, [createPost])
return (
<div className="home">
<div style={{display: 'flex', alignItems: 'center'}}>
<h1>this is the home: Welcome, {userData.username}</h1>
<Link style={{margin: 10}} to="/home">home</Link>
<Link style={{margin: 10}} to="/profile">profile</Link>
<Link style={{margin: 10}} onClick={handleToken} to="/">log out</Link>
</div>
<form onSubmit={handleOnSubmit}>
<input type="text" placeholder="What's happening?" value={createPost} onChange={e => setCreatePost(e.target.value)}/>
<button type="submit">tweet</button>
</form>
<div style={{display: 'flex', flexDirection: 'column'}}>
{posts.map(post => (
<div style={{border: '2px solid black', marginBottom: 10, marginRight: 'auto', marginLeft: 'auto', width: 300}} key={post._id}>
<div style={{display: 'flex', alignItems: 'center'}}>
<Avatar src={post.avatar}/>
<span style={{color: 'blue', marginLeft: 10}}>{post.name} <span style={{color: 'grey', fontSize: 11}}>@{post?.username}</span></span><br/>
</div>
<span>{post.textOfThePost}</span><br/>
<span>{moment(post.date).format('lll')}</span>
</div>
)).reverse()}
</div>
</div>
)
}
函数Home(){
const{userData,setUserData}=useContext(userContext)
const[posts,setPost]=useState([]
常量[createPost,setCreatePost]=useState(“”)
常量handleToken=()=>{
localStorage.removietem('auth-token')
}
const-token=localStorage.getItem(“auth-token”);
const handleOnSubmit=(e)=>{
e、 预防默认值()
轴心柱http://localhost:5000/posts“,{textofpost:createPost}{
标头:{'auth token':token},
})
.然后((res)=>{setCreatePost(“”})
}
useffect(()=>{
axios.get()http://localhost:5000/posts')
。然后(res=>{
setPost(恢复数据)
})
},[createPost])
返回(
这是家:欢迎,{userData.username}
家
轮廓
注销
setCreatePost(e.target.value)}/>
推特
{posts.map(post=>(
{post.name}@{post?.username}
{post.textofpost}
{moment(post.date).format('lll')}
)).reverse()}
)
}
您只将令牌
存储在本地存储
中,因此没有理由同时保存上下文
如果确实要保存用户数据
,可以将其保存在本地存储
(或使用任何其他状态管理方式):
函数登录(){
//无关代码
const handleOnSubmit=(e)=>{
e、 预防默认值()
axios.post(“http://localhost:5000/login“,登录用户)
。然后((res)=>{
const{name,lastname,username,email}=res.data.user;
const newUserData={name,lastname,username,email};
setUserData(newUserData);
setItem('user-data',JSON.stringify(newUserData));
//无关代码
});
}
//无关代码
}
然后在App
的useState
调用中使用它:
函数应用程序(){
const persistentUserData=localStorage.getItem('user-data');
const[userData,setUserData]=useState(JSON.parse(persistentUserData));
//返回
}
此类JS应用程序中的状态在页面刷新之间不会自动保持。因此需要localstorage/sessionstorage/indexdb和类似的机制。您需要保存状态并在组件加载时检索它
例如,您可以使用如下钩子修改home
组件以保存/检索数据:
function App() {
// 1. Create a key to name your data in local storage
const USER_DATA_KEY_IN_LOCALSTORAGE = 'user_data';
const [userData, setUserData] = useState({
name: "",
lastname: "",
username: "",
email: "",
});
// 2. Retrieve userData from local storage on startup
useEffect(() => {
const userDataString = window.localStorage.getItem(USER_DATA_KEY_IN_LOCALSTORAGE);
setUserData(JSON.parse(userDataString));
}, []);
// 3. Update userData in local storage when it changes.
useEffect(() => {
window.localStorage.setItem(USER_DATA_KEY_IN_LOCALSTORAGE, JSON.stringify(userData));
}, [userData]);
return (
<Router>
<userContext.Provider value={{ userData, setUserData }}>
<div className="app">
<Switch>
<Route exact path="/" component={Login} />
<Route path="/register" component={Register} />
<Route path="/home" component={Home} />
<Route path="/profile" component={Profile} />
</Switch>
</div>
</userContext.Provider>
</Router>
);
}
函数应用程序(){
//1.创建密钥以命名本地存储中的数据
const USER_DATA_KEY_IN_LOCALSTORAGE='USER_DATA';
const[userData,setUserData]=useState({
姓名:“,
姓氏:“,
用户名:“”,
电邮:“,
});
//2.启动时从本地存储中检索用户数据
useffect(()=>{
const userDataString=window.localStorage.getItem(localStorage中的USER\u DATA\u KEY\u);
setUserData(JSON.parse(userDataString));
}, []);
//3.当用户数据发生变化时,更新本地存储中的用户数据。
useffect(()=>{
setItem(USER_DATA_KEY_IN_localStorage,JSON.stringify(userData));
},[userData]);
返回(
);
}
当然,您需要处理用户数据不存在、JSON.parse()抛出错误和类似内容的情况。非常感谢!我把用户数据放在本地存储之前,似乎我错过了你在app.js中所做的事情。现在它开始工作了