class BublePlugin {
  apply(compiler) {
    compiler.plugin('emit', (compilation, callback) => {
      compilation.chunks.forEach(chunk => {
        chunk.files.forEach(function(filename) {
          if (/\.js$/.test(filename)) {
            const source = compilation.assets[filename].source()
                , __buble = buble.transform(source)
            compilation.assets[filename] = {
              source() {
                return __buble.code
              },
              size() {
                return __buble.code.length
              }
            }
          }
        })
      })
      callback()
    })
  }
}