Webpack with babel-loader not emitting valid es5

Question

I have a webpack config that is based off https://github.com/vuejs-templates/webpack-simple/blob/master/template/webpack.config.js It uses vue-loader and babel-loader. The issue is I cannot get it to generate ES5 code so that it will work in the most broad range of clients.

If I use the ES2015 preset, webpack.optimize.UglifyJsPlugin fails to minify the output because Uglify can only handle ES5 (not counting the harmony branch). The errors are similar to: Unexpected token: punc (() and occur in multiple files.

I can work around this by using babili-webpack-plugin which will minify the ES6 code but is very slow. However, when I deploy this code, I see errors being reported back saying Block-scoped declarations (let, const, function, class) not yet supported outside strict mode so I know they are older clients choking on ES6 code.

How can I get proper ES5 code output from babel-loader? I have tried multiple presets, with or without the transform-runtime plugin. Config below:

const webpack = require('webpack');
const globEntries = require('webpack-glob-entries');
const _ = require('lodash');
const path = require('path');
const BabiliPlugin = require("babili-webpack-plugin");

const env = process.env.NODE_ENV;

let entries;
if (env === 'production') {
  entries = globEntries('./src/**/vue/*.js');
} else {
  entries = _.mapValues(globEntries('./src/**/vue/*.js'), entry => [entry, 'webpack-hot-middleware/client?reload=true']);
}

module.exports = {
  entry: entries,
  output: {
    path: '/', ///no real path is required, just pass "/"
    publicPath: '/vue',
    filename: '[name].js',
  },
  module: {
    rules: [
      {
        test: /\.vue$/,
        loader: 'vue-loader',
        options: {
          loaders: {
            scss: 'vue-style-loader!css-loader!sass-loader',
            sass: 'vue-style-loader!css-loader!sass-loader?indentedSyntax',
          },
          // other vue-loader options go here
        },
      },
      {
        test: /\.js$/,
        exclude: /node_modules/,
        use: {
          loader: 'babel-loader',
          query: {
            presets: ['es2015'],
            plugins: ['transform-runtime'],
          },
        },
      },
      {
        test: /\.(png|jpg|gif|svg)$/,
        loader: 'file-loader',
        options: {
          name: '[name].[ext]?[hash]',
        },
      },
    ],
  },
  resolve: {
    alias: {
      vue$: 'vue/dist/vue.esm.js',
    },
  },
  plugins: [
    new webpack.HotModuleReplacementPlugin(), // Enable HMR
    new webpack.NoEmitOnErrorsPlugin(),
  ],
  performance: {
    hints: false,
  },
  devtool: '#eval-source-map',
};

if (env === 'staging' || env === 'production') {
  //module.exports.devtool = env === 'staging' ? '#source-map' : false;
  module.exports.devtool = '#source-map';
  module.exports.output.path = path.resolve(__dirname, './src/v1/parse/cloud/public/vue');
  // http://vue-loader.vuejs.org/en/workflow/production.html
  module.exports.plugins = (module.exports.plugins || []).concat([
    new webpack.DefinePlugin({
      'process.env': {
        NODE_ENV: `"${env}"`,
      },
    }),
    new webpack.optimize.UglifyJsPlugin({
      sourceMap: true,
      compress: {
        warnings: false,
      },
    }),
    // new BabiliPlugin(),
    new webpack.LoaderOptionsPlugin({
      minimize: true,
    }),
  ]);
}

Answer 1

vue-loader will process your js with babel-loader (if it's detected), and uses .babelrc by default.

In your current setup you are not passing any options to Babel when it is used by vue-loader (meaning Babel uses no rules for your Vue files).

Either create .babelrc or specify the js loader by yourself for the .vue files to provide it with options:

{
  test: /\.vue$/,
  loader: 'vue-loader',
  options: {
    loaders: {
      js: 'babel?presets[]=es2015' // Pass parameters as options
    }
  }
}

The env preset for Babel has an uglify option that will fully compile to ES5. This preset is recommended practice to keep your environment up to date.

// .babelrc
{
  "presets": [
    [ "env", { "uglify": true } ],
    "stage-1" // Or other presets not included with 'env' preset.
  ],
  "plugins": ["transform-runtime"]
}

Instead of using preset es2015 only, you might add es2016 and es2017, as well as stage-4, stage-3, etc. to assure all your code is transformed, and not just the ES2015 parts.