const Module = module.constructor

const mfs = new MemoryFs
const serverCompiler = webpack(serverConfig)
serverCompiler.outputFileSystem = mfs
let serverBundle
serverCompiler.watch({},(err,stats) => {
    if(err) throw err
    stats = stats.toJson()
    stats.errors.forEach(err => console.error(err))
    stats.warnings.forEach(warn => console.warn(warn))

    const bundlePath = path.join(
        serverConfig.output.path,
        serverConfig.output.filename
    )

    const bundle = mfs.readFileSync(bundlePath,'utf-8')
    const m = new Module()
    m._compiler(bundle,'server-entry.js')
    serverBundle = m.default
})

跟着视频一步步来的，webpack是4.启动dev:server时报错，m._compiler is not a function