Skip to main content

no-floating-message-channels

Require MessageChannel ports to be retained so they can be closed.

Rule catalog ID: R012

Targeted pattern scopeโ€‹

This rule targets browser MessageChannel constructors:

  • MessageChannel
  • window.MessageChannel
  • self.MessageChannel
  • globalThis.MessageChannel

The rule reports channel instances that are immediately discarded or whose port1/port2 properties are accessed directly from the temporary channel object. Keeping only one inline port loses the peer port and makes full teardown ambiguous.

What this rule reportsโ€‹

The rule reports:

  • standalone channel construction such as new MessageChannel();
  • voided channel construction such as void new MessageChannel();
  • immediate port sends such as new MessageChannel().port1.postMessage(message);
  • retaining a single inline port such as const port = new MessageChannel().port1;

It intentionally does not require same-function close() calls. Ownership can be transferred to a component instance, channel manager, returned value, or both destructured MessagePort handles.

Why this rule existsโ€‹

MessageChannel creates two linked MessagePort handles. MessagePort.close() disconnects a port so it is no longer active. If the channel object is discarded or only one port is retained from an inline expression, code cannot reliably close both sides of the channel during cleanup.

Incorrectโ€‹

new MessageChannel();
void new MessageChannel();
new MessageChannel().port1.postMessage(message);
const port = new MessageChannel().port2;

Correctโ€‹

const channel = new MessageChannel();

channel.port1.addEventListener("message", onMessage);
channel.port1.close();
channel.port2.close();
const { port1, port2 } = new MessageChannel();

port1.postMessage(message);
port1.close();
port2.close();
return new MessageChannel();
registerChannel(new MessageChannel());

Behavior and migration notesโ€‹

Store either the MessageChannel object or both MessagePort handles in the owner that will close them. For UI code, that owner is usually a component, worker bridge, route lifecycle, or application-level channel manager.

This rule does not autofix. Introducing a variable without selecting the owner and teardown point would hide the lifecycle problem instead of solving it.

ESLint flat config exampleโ€‹

import runtimeCleanup from "eslint-plugin-runtime-cleanup";

export default [
    runtimeCleanup.configs.recommended,
];

When not to use itโ€‹

Do not enable this rule for code that intentionally creates runtime-lifetime message ports and does not need explicit teardown. Prefer a narrow disable comment with a reason when a channel is meant to live for the whole runtime.

Further readingโ€‹