code: function sendMsg(type, data) {
    if (
      typeof self !== 'undefined' &&
      (typeof WorkerGlobalScope === 'undefined' ||
        !(self instanceof WorkerGlobalScope))
    ) {
      self.postMessage(
        {
          type: `webpack${type}`,
          data,
        },
        '*'
      );
    }
  }
docs: Send messages to the outside, so plugins can consume it.