Possible regression in 0.4.4

[dustinsoftware]

I can't repro this issue outside of my work's source code (which I can't share), so I understand having this fixed is a bit of a longshot. That said, I'll share as much as I can about the problem we're running into:

In #284 , this.id was set to empty string in the constructor. Somehow, in one of our projects, this causes React to be imported as undefined in a lazy loaded component.

After using yarn link locally with mini-css-extract-plugin, I can confirm that the issue did not happen before that change for us. Commenting out the initial assignment to this.id and rebuilding fixes the runtime issue.

Our project looks something like this:

• Main component
  • Lazy loaded component, whose source is minified and published to an internal npm registry
  • Lazy loaded component's exported stylesheet

export class LazyLoaded extends React.Component {
	constructor() {
		super();
		this.state = { loaded: false };
	}
	componentDidMount() {
		import('lazy-loaded-example').then(component => { this.setState({ loadedComponent: component.default })})
	}
	render() {
		return this.state.loadedComponent
			? React.createElement(this.state.loadedComponent, {})
			: React.createElement('h1', {}, 'Loading');
	}
}

After change:

I can repro this pretty reliably locally, but I'm not sure what information I could share that would be helpful.

  "devDependencies": {
    "css-loader": "^1.0.0",
    "mini-css-extract-plugin": "^0.4.5",
    "postcss-loader": "^3.0.0",
    "url-loader": "^1.1.2",
    "webpack": "^4.16.0",
    "webpack-cli": "^3.0.8"
  },
  "scripts": {
    "build": "webpack"
  },

[dustinsoftware]

Ok, it looks like this issue is related NamedModulesPlugin using a strict equality check, comparing id to null somewhere around here.

webpack/webpack#7088
https://github.com/webpack/webpack/pull/7152/files

Should this.id be initialized to null in MiniCssExtractPlugin, if at all? It's still unclear why that change was introduced.

cc @lfre @sokra do you have any ideas off the top of your head where to investigate next? For now we'll work around the problem by pinning to an older version of this plugin.

[alexander-akait]

@dustinsoftware problem solved in webpack@5, don't think it is possible to fix on plugin side

[alexander-akait]

/cc @dustinsoftware sorry for big delay, problem still exists? Can you create minimum reproducible test repo?

[dustinsoftware]

Sorry, I’ve since moved on to another co and don’t have a reliable repro for this anymore. I think we worked around the problem by pinning to an older package version.