If the Node.js process is spawned with an IPC channel (see the [Child Process][]
and [Cluster][] documentation), the 'message' event is emitted whenever a
message sent by a parent process using [childprocess.send()][] is received by
the child process.
The listener callback is invoked with the following arguments:
message{Object} a parsed JSON object or primitive value.sendHandle{Handle object} a [net.Socket][] or [net.Server][] object, or undefined.
Note: The message goes through JSON serialization and parsing. The resulting
message might not be the same as what is originally sent. See notes in
[the JSON.stringify() specification][JSON.stringify spec].