Element type is invalid: expected a string (for built-in components) or a class/function (for compos

1、错误描述

2、错误原因

import React from 'react';
import ReactDOM from 'react-dom';
import Column2D from './components/Column2D.js'

import logo from './logo.svg';
import './App.css';

function App() {
  return (
   <Column2D/>
  );
}

export default App;

     在调用返回值时，没有调用界面上的DOM元素，应添加一个document.getElementById()

3、解决办法

import React from 'react';
import ReactDOM from 'react-dom';
import Column2D from './components/Column2D.js'

import logo from './logo.svg';
import './App.css';

function App() {
  return (
   <Column2D/>,
	 document.getElementById("root")
  );
}

export default App;