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MonDisconnect
Bun

method

Spawn.BaseOptions.onDisconnect

onDisconnect(): void | Promise<void>;

Called exactly once when the IPC channel between the parent and this subprocess is closed. After this runs, no further IPC messages will be delivered.

When it fires:

  • The child called process.disconnect() or the parent called subprocess.disconnect().
  • The child exited for any reason (normal exit or due to a signal like SIGILL, SIGKILL, etc.).
  • The child replaced itself with a program that does not support Bun IPC.

Notes:

  • This callback indicates that the pipe is closed; it is not an error by itself. Use onExit or Subprocess.exited to determine why the process ended.
  • It may occur before or after onExit depending on timing; do not rely on ordering. Typically, if you or the child call disconnect() first, this fires before onExit; if the process exits without an explicit disconnect, either may happen first.
  • Only runs when ipc is enabled and runs at most once per subprocess.
  • If the child becomes a zombie (exited but not yet reaped), the IPC is already closed, and this callback will fire (or may already have fired).
const subprocess = spawn({
 cmd: ["echo", "hello"],
 ipc: (message) => console.log(message),
 onDisconnect: () => {
   console.log("IPC channel disconnected");
 },
});