ref="dart-isolate/Isolate/beforeNextEvent-constant.html">beforeNextEvent</a>.
The response is sent at different times depending on the ping type:</p><ul><li><code>immediate</code>: The isolate responds as soon as it receives the
  control message. This is after any previous control message
  from the same isolate has been received and processed,
  but may be during execution of another event.</li><li><code>beforeNextEvent</code>: The response is scheduled for the next time
  control returns to the event loo