webpack babel-loader将jsx转换为js错误：build failed SyntaxError ~main.js Unexpected token

React+Webpack，在webpack中使用babel-loader将jsx转换为js错误，错误信息如下：

ERROR in ./app/main.js
Module build failed: SyntaxError: ~/**/app/main.js: Unexpected token (2:13)
  1 | var React = require("react");
> 2 | React.render(<h1>hello world</h1>,document.getElementById("app"));
    |              ^
at Parser.pp.raise (~/**/node_modules/babylon/lib/parser/location.js:24:13)

webpack.config.js配置文件如下：

var path = require('path');
module.exports = {
  entry: ['webpack/hot/dev-server',path.resolve(__dirname, 'app/main.js')],
  output: {
    path: path.resolve(__dirname, 'build'),
    filename: 'bundle.js'
  },
  module: {
      loaders: [
          { test: /\.js$/, exclude: /node_modules/, loader: "babel-loader"}
      ]
  }
};

解决办法如下：

添加babel-preset-react：

npm install babel-preset-react

然后在webpack.config.js中添加presets选项到babel-loader，或也可以添加到.babelrc或package.js，参考：https://babeljs.io/docs/en/config-files/。下面是webpack.config.js的配置：

{ 
    test: /\.jsx?$/,         //同时匹配.js和.jsx文件
    exclude: /node_modules/, 
    loader: "babel", 
    query:
      {
        presets:['react']
      }
}

特别注意，Webpack4使用如下方式：

npm install babel-loader babel-preset-react

webpack配置如下：

{
    test: /\.jsx?$/,
    exclude: /node_modules/,
    use: [
      {
        loader: 'babel-loader',
        options: {
          presets: ['react']
        }
      }
    ],
  }