Bug: using MessageChannel prevents node.js process from exiting

[just-boris]

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Edited: Here's how to fix this: #20756 (comment).

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React version: 17.0.1 (latest)

Steps To Reproduce

This code finishes properly in node.js 14, but holds the process open in node.js 15

global.window = global; // simulate JSDOM
require('scheduler');

Since node.js 15, there is a global MessageChannel object now, which prevents node event loop from exiting. To let the process shut down properly, it should either call port.close() or port.unref()

This becomes an issue when testing React code within JSDOM environment, as the test process cannot exit properly.

The current behavior

The process with JSDOM tests never finishes

The expected behavior

The process finishes properly

[rickhanlonii]

Nice find! Do you want to submit a PR to fix?

[patil2097]

I would love to help you on fixing this problem.Can you guide me in submitting a fix? I am really new to open source. @rickhanlonii

[amensum]

@rickhanlonii
Can I take this issue for try to fix it and send PR?

[amensum]

Issue example:

var { JSDOM } = require('jsdom')

var { window } = new JSDOM()

global.window = window
global.document = window.document

require('scheduler')

[rickhanlonii]

Hey all, anyone can take this issue, I'll review the first PR.

The problem is that this feature detection is too naive. In node environments, we should use unstable_no_dom and in browser environments we should use the browser scheduler.

[gaearon]

We're going with #20834 as a likely fix in 17.1.0, but it will need more testing.