Fix ES module for Node.js

[denysoblohin-okta]

Issue:
Can't import broadcast-channel as ES module for Node.js.

import { BroadcastChannel } from 'broadcast-channel';
         ^^^^^^^^^^^^^^^^
SyntaxError: Named export 'BroadcastChannel' not found. The requested module 'broadcast-channel' is a CommonJS module, which may not support all module.exports as named exports.
CommonJS modules can always be imported via the default export, for example using:

import pkg from 'broadcast-channel';
const { BroadcastChannel } = pkg;

    at ModuleJob._instantiate (internal/modules/esm/module_job.js:124:21)
    at async ModuleJob.run (internal/modules/esm/module_job.js:179:5)
    at async Loader.import (internal/modules/esm/loader.js:178:24)
    at async Object.loadESM (internal/process/esm_loader.js:68:5)
    at async handleMainPromise (internal/modules/run_main.js:59:12)

Steps to reproduce: create simple project with index.mjs (having just 1 line with import of broadcast-channel) and try to run node index.mjs

Solution:

• Use .mjs extensions for ESM module. (Don't add type: "module" in package.json because we want to support both ESM and CJS)
• Add testing ESM and CJS modules

More details here: https://github.com/sheremet-va/dual-packaging

[denysoblohin-okta]

@pubkey Can you review please?

[pubkey]

Please do not check in generated files from the dist folder. This makes the PR unreadable.

[denysoblohin-okta]

@pubkey Done

[pubkey]

Hmm, the CI fails.
But it also fails on master.
Looks like a timing problem where github actions now gives a slower server then before.

[denysoblohin-okta]

@pubkey Probably need to increase this constant:

broadcast-channel/test/integration.test.js

Lines 550 to 551 in c872596

	if (t > 50) {
	throw new Error('this should never happen');

Should I fix this to make CI pass?

[pubkey]

Yes please.

[denysoblohin-okta]

@pubkey Done. CI passes. Please approve workflow for PR.

[pubkey]

Merged and released.
Thank you.