Uglifyjs fix

[ocboogie]

Note: I'm not quite sure if Preact is the problem.

I came across a problem using react-slick and preact. I got a Uncaught TypeError: Cannot read property 'className' of undefined, but the odd thing was I only got this error in production mode. So I looked into it and it turns out preact-compat wasn't mutating the VNode. And the reason for that was Uglifyjs was not exposing VNode anymore. Since VNode is an empty class and only used once, in the h function, Uglifyjs makes it inline, like let p = new function() {}(); so preact-compat can't access it.

You can see this issue in action here.

So my fix(hack) for this issue was setting a property on VNode after it was declared, this way Uglifyjs doesn't make it inline. They're very well might be a more elegant way to fix this.

[coveralls]

Coverage remained the same at 100.0% when pulling 50a6f41 on ocboogie:uglifyjs-fix into 3e69287 on developit:master.

[yaodingyd]

Did you try using preact-compat? I think this line https://github.com/developit/preact-compat/blob/master/src/index.js#L41 covers your issue.

[ocboogie]

@yaodingyd Unfortunately that's not the case. Since the VNode class is inline in the h function, it creates a new class each time h is ran. So when preact-compat is mutating the constructor, it only mutates that Instance.

I added an example in my test environment here. This will log true.

[yaodingyd]

@ocboogie Just realize I didn't fully read your first comment. My bad! Will investigate more.

[ocboogie]

Just so you know the compression option that's causing problems is the unused option. You can see it here. And you can disable it in the Webpack config here.

[kaisermann]

What version of uglifyjs are you using? If it's >= 3, turn off the compress.reduce_funcs options and see if it works.

[yaodingyd]

It looks like setting either unused or reduce_funcs to false both works.

[developit]

I would prefer to solve this by documenting the issue - adding weight and cost to Preact to fix an Uglify bug isn't something we can do. Anyone want to take a swing at adding it to the docs?

[developit]

Anyone know if source position matters to Uglify here? Also is there an upstream bug we can track to know when Uglify fixes this?

[developit]

Hi all! This was fixed in Preact 8.3.0 thanks to @wardpeet's clever trick (#1153).