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Communicate with a child process over IPC

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Pipes carry bytes, but coordinating with a worker process is easier with structured messages. Deno supports the Node.js IPC channel through node:child_process fork. This example forks itself and exchanges messages with the child.

import { fork } from "node:child_process";
import process from "node:process";
In the child, process.send exists. The child answers each message it receives and exits when asked.
if (process.send) {
  process.on("message", (message) => {
    if (message === "stop") {
      process.exit(0);
    }
    process.send!({ answer: `pong: ${message}` });
  });
} else {
In the parent, fork starts the child with an IPC channel attached. Forking this same file keeps the example self-contained; normally the child is its own module.
  const child = fork(new URL(import.meta.url).pathname);
Messages from the child arrive on the message event. They are structured values, not bytes, so no parsing is needed.
  child.on("message", (message) => {
    console.log("from child:", JSON.stringify(message)); // {"answer":"pong: ping"}
    child.send("stop");
  });
Send a message to the child to start the exchange.
  child.send("ping");
The parent finishes when the child exits.
  child.on("exit", (code) => {
    console.log(`child exited with code ${code}`); // child exited with code 0
  });
}

Run this example locally using the Deno CLI:

deno run -A https://docs.deno.com/examples/scripts/child_process_ipc.ts

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