Question

元素类型无效：预期为字符串（对于内置组件）或类/函数（对于复合组件），但得到：未定义。您可能忘记了从定义文件中导出组件，或者可能混淆了默认导入和命名导入。

检查App的呈现方法。

为什么会出现此错误？

index.js

import ReactDOM from 'react-dom';
import { makeMainRoutes } from './routes';

const routes = makeMainRoutes();

ReactDOM.render(
  routes,
  document.getElementById('root')
);

routes.js

import React from 'react';
import { Route, Router } from 'react-router-dom';
import App from './App';
import Home from './Home/Home';
import Callback from './Callback/Callback';
import Auth from './Auth/Auth';
import history from './history';

const auth = new Auth();

const handleAuthentication = (nextState, replace) => {
  if (/access_token|id_token|error/.test(nextState.location.hash)) {
    auth.handleAuthentication();
  }
}

export const makeMainRoutes = () => {
  return (
    <Router history={history} component={App}>
      <div>
        <Route path="/" render={(props) => <App auth={auth} {...props} />} />
        <Route path="/home" render={(props) => <Home auth={auth} {...props} />} />
        <Route path="/callback" render={(props) => {
          handleAuthentication(props);
          return <Callback {...props} /> 
        }}/>
      </div>
    </Router>
  );
}

App.js

import React, { Component } from 'react';
import { Navbar, Button } from 'react-bootstrap';
import './App.css';

class App extends Component {
  goTo(route) {
    this.props.history.replace(`/${route}`)
  }

  login() {
    this.props.auth.login();
  }

  logout() {
    this.props.auth.logout();
  }

  componentDidMount() {
    const { renewSession } = this.props.auth;

    if (localStorage.getItem('isLoggedIn') === 'true') {
      renewSession();
    }
  }

  render() {
    const { isAuthenticated } = this.props.auth;

    return (
      <div>
        {/* <script type="text/javascript" src="node_modules/auth0-js/build/auth0.js"></script> */}
        {/* <script src="https://cdn.auth0.com/js/auth0/9.10/auth0.min.js"></script> */}

        <Navbar fluid>
          <Navbar.Header>
            <Navbar.Brand>
              <a href="#">Auth0 - React</a>
            </Navbar.Brand>
            <Button
              bsStyle="primary"
              className="btn-margin"
              onClick={this.goTo.bind(this, 'home')}
            >
              Home
            </Button>
            {
              !isAuthenticated() && (
                  <Button
                    id="qsLoginBtn"
                    bsStyle="primary"
                    className="btn-margin"
                    onClick={this.login.bind(this)}
                  >
                    Log In
                  </Button>
                )
            }
            {
              isAuthenticated() && (
                  <Button
                    id="qsLogoutBtn"
                    bsStyle="primary"
                    className="btn-margin"
                    onClick={this.logout.bind(this)}
                  >
                    Log Out
                  </Button>
                )
            }
          </Navbar.Header>
        </Navbar>
      </div>
    );
  }
}

export default App;

Answer 1

undefined && whatever解析为undefined。检查this.props.auth.isAuthenticated()返回的值。应该是布尔值。您可以使用!!来解决此问题：

        {
          !!isAuthenticated() && (
              <Button
                id="qsLogoutBtn"
                bsStyle="primary"
                className="btn-margin"
                onClick={this.logout.bind(this)}
              >
                Log Out
              </Button>
            )
        }

但是由于您必须对此条件进行替代，因此最好只使用以下代码：

        {
          isAuthenticated() ? (
              <Button
                id="qsLogoutBtn"
                bsStyle="primary"
                className="btn-margin"
                onClick={this.logout.bind(this)}
              >
                Log Out
              </Button>
            ) : (
              <Button
                id="qsLoginBtn"
                bsStyle="primary"
                className="btn-margin"
                onClick={this.login.bind(this)}
              >
                Log In
              </Button>
            )
        }

元素类型无效：需要一个字符串（用于内置组件）......检查“ App”的渲染方法

1 个答案: