警告：React.createElement：类型无效——需要一个字符串

Question

I'm a complete beginner at web development + react, and am running into a problem as I try to render an imported component.

I'm trying to render the following component: https://www.npmjs.com/package/react-launch-gauge

However, when i run, i keep getting the following error:

> Warning: React.createElement: type is invalid -- expected a string (for built-in components) or a class/function (for composite components) but got: object.

What am I doing wrong? My code is below

App.jsx

import React from 'react';
import Gauge from 'react-launch-gauge';

class App extends React.Component {
    constructor(props, context) {
        super(props, context)
    }
    render() {
        return (
            <div>
                <Gauge title={'Points'} value={42} max={100} />
            </div>
        );
    }
}
export default App;

main.js

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App.jsx';

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

webpack.config.js

var config = {
   entry: './main.js',
   output: {
      path:'/',
      filename: 'index.js',
   },
   devServer: {
      inline: true,
      port: 8080
   },
   module: {
      loaders: [
         {
            test: /\.jsx?$/,
            exclude: /node_modules/,
            loader: 'babel-loader',
            query: {
               presets: ['es2015', 'react']
            }
         }
      ]
   }
}
module.exports = config;

package.json

{
  "name": "iw",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "webpack-dev-server --hot"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "babel-core": "^6.26.0",
    "babel-loader": "^7.1.2",
    "babel-preset-es2015": "^6.24.1",
    "babel-preset-react": "^6.24.1",
    "react": "^16.2.0",
    "react-dom": "^16.2.0",
    "react-launch-gauge": "^0.2.3",
    "webpack": "^3.11.0",
    "webpack-dev-server": "^2.11.1"
  }
}

Answer 1

I believe you'd need to supply constructor to properly initialize App Component, like so:

App.jsx

import React from 'react';
import Gauge from 'react-launch-gauge';

class App extends React.Component {
    constructor(props, context) {
        super(props, context)
    }

    render() {
        return (
            <div>
                <Gauge title={'Points'} value={42} max={100} />
            </div>
        );
    }
}
export default App;

Answer 2

I have meet same problem like you, this reason is that Gauge has not defined. so you must definde it with basic structure and export it , you will solve it

and like this