【已解决】ERROR in xx.js from UglifyJs Invalid assignment ./node_modules/@vant/xx.mjs

npm run build时，报如下错：

.babelrc文件如下：

{
  "presets": [
    ["env", {
      "modules": false,
      "targets": {
        "browsers": ["> 1%", "last 2 versions", "not ie <= 8"]
      }
    }],
    "stage-2"
  ],
  "plugins": [
    ["import", {
      "libraryName": "vant",
      "libraryDirectory": "es",
      "style": true
    }],
    "transform-runtime"
  ],
  "env": {
    "test": {
      "presets": ["env", "stage-2"],
      "plugins": ["istanbul"]
    }
  }
}

解决方案：在webpack.base.conf.js文件里

      
      {
        test: /\.js$/,
        loader: 'babel-loader',
        include: [resolve('src'), resolve('test')]
      },
      // 把如上注释掉，改为如下即可
      {
        test: /\.(js|mjs)$/,
        loader: 'babel-loader',
        include: [resolve('src'), resolve('test'), resolve('node_modules/@vant')]
      },