reactjs - Uncaught Error : Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: object

Question

Reactjs 上下文提供程序错误

我收到以下错误

invariant.js:42 Uncaught Error: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: object.

这是我的app.js

import React from 'react';
import ReactDOM from 'react-dom';
import { UserProvider } from "./lib/user.js"

const App = () => <UserProvider></UserProvider>

ReactDOM.render(
  <App />,
  document.getElementById("app")
);

这是./lib/user.js:

import React from 'react'

export const UserContext = React.createContext({
  user: null,
  logIn: ((token, user) => {}),
  logOut: (() => {})
})

export class UserProvider extends React.Component {
  constructor(props) {
    super(props)

    this.logIn = (token, user) => {
      setToken(token)
      this.setState(state => ({user: user}))
    }

    this.logOut = (client) => {
      clearToken()
      this.setState(state => ({user: null}))
      client.resetStore()
      client.cache.reset()
    }

    this.state = {
      user: null,
      logIn: this.logIn,
      logOut: this.logOut
    }
  }

  render() {
    console.log(<div></div>)
    console.log(<UserContext.Provider/>)
    return (
      <UserContext.Provider value={this.state}>
        <p>hi</p>
      </UserContext.Provider>
    )
  }
}

这是在 React 16.3.2 上。在很多情况下，错误是由于默认导出与命名导出引起的，但这似乎不是:

1. Uncaught Error: Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function but got: object
2. Uncaught Error: Element type is invalid: expected a string (for built-in components)
3. Element type is invalid: expected a string (for built-in components) or a class/function

Answer 1

您可能正在将 react@16.3 与尚不支持上下文的早期 react-dom 版本(例如 16.2)一起使用。