React Class如何在promise fetch调用后返回布尔值

Question

你好我有这个类，当我从另一个组件调用 Auth.isAuthenticated() 时，它总是返回 false（它的默认值），即使服务器返回 200 响应，女巫设置 this.authenticated = true 。 如何使用 promise 让方法等到 fetch 调用完成然后返回结果

编辑： 我需要返回布尔值真或假，因此基于此，我可以显示或隐藏组件，所有答案都有帮助，但我需要布尔值而不是承诺任何帮助

    class Auth {
    constructor() {
        this.authenticated = false;
    }


    isAuthenticated() {
        //get token from local storage if there is one
        const jwttoken = localStorage.getItem('jwttoken');
        const bearer = 'Bearer ' + jwttoken;
        const data = new FormData();
        // get the website backend main url from .env
        const REACT_APP_URL = process.env.REACT_APP_URL
        fetch(`${REACT_APP_URL}/api/auth/verify`, {
            method: 'POST',
            headers: {
                'Accept': 'application/json',
                'Authorization': bearer,
            },
            body: data
        }).then(
            (response) => {
                response.json()
                    .then((res) => {
                        if (response.status === 200) {
                            this.authenticated = true;
                        }
                        if (response.status === 401) {
                            localStorage.removeItem('jwttoken');
                            this.authenticated = false;
                        }
                    })
            }
        ).catch((err) => {
            // console.log(err)
        });

        return this.authenticated;
    }


}



export default new Auth();

我从另一个组件调用 Auth.isAuthenticated() === true

export const PrivateRoute = ({ component: Component, ...rest }) => {

  return (
    <Route {...rest} render={(props) => (
      Auth.isAuthenticated() === true
        ? <Component {...props} />
        : <Redirect to='/admin' />
    )} />
      )
}

Answer 1

假设您要编写一个函数，该函数返回一个承诺并在某些操作完成时解析（例如 API 调用）。你可以这样写：

const myAsyncFunction = () =>{
    return new Promise((resolve, reject) =>{
        //Faking an API Call
        setTimeout(() => resolve('data'), 400)
    })
}

给你！现在你有一个函数可以返回一个承诺，该承诺将在 400 毫秒内解决。现在您需要使用.then() 方法或async await 语句。

const sideEffects = async () =>{
    const result = await myAsyncFunction()
    console.log(result) //'data'
}

Answer 2

如果你不想做async/await，你可以让isAuthenticated返回一个承诺。

isAuthenticated() {
  return new Promise((resolve, reject) => {
    //get token from local storage if there is one
        const jwttoken = localStorage.getItem('jwttoken');
        const bearer = 'Bearer ' + jwttoken;
        const data = new FormData();
        // get the website backend main url from .env
        const REACT_APP_URL = process.env.REACT_APP_URL
        fetch(`${REACT_APP_URL}/api/auth/verify`, {
            method: 'POST',
            headers: {
                'Accept': 'application/json',
                'Authorization': bearer,
            },
            body: data
        }).then(
            (response) => {
                response.json()
                    .then((res) => {
                        if (response.status === 200) {
                            resolve(true)
                        }
                        if (response.status === 401) {
                            localStorage.removeItem('jwttoken');
                            resolve(false)
                        }
                    })
            }
        ).catch((err) => {
            // reject(err)
        });
  })        
}

在异步函数内部你可以使用let isAuthenticated = await isAuthenticated() 或者你可以在异步函数外部使用.then 和.catch 来返回结果

Answer 3

使用等待异步

async isAuthenticated() {
        //get token from local storage if there is one
        const jwttoken = localStorage.getItem('jwttoken');
        const bearer = 'Bearer ' + jwttoken;
        const data = new FormData();
        // get the website backend main url from .env
        const REACT_APP_URL = process.env.REACT_APP_URL
        const response = await fetch(`${REACT_APP_URL}/api/auth/verify`, {
            method: 'POST',
            headers: {
                'Accept': 'application/json',
                'Authorization': bearer,
            },
            body: data
        });

        const responseToJson = await response.json();

         if (responseToJson.status === 200) {
             this.authenticated = true;
         }
         if (responseToJson.status === 401) {
             localStorage.removeItem('jwttoken');
             this.authenticated = false;
         }

       return this.authenticated;
    }