preactjs / legacy-compat Goto Github PK

The legacy-compat package in ESM mode does not appear to place nicely with other legacy versions of libraries -- I ran into runtime issues in react-redux and also several other code paths in our codebase.

Per discussion in Slack, legacy-compat isn't tree-shakeable, so we don't gain anything significantly from trying to resolve the compatibility issues.

Referencing an original issue from the Preact repo here:

preactjs/preact#492

The core HTML spec doesn't allow for this stuff, and it appears that React v15 transforms them into style tags (100%) or removes the unit (50px).

Same issue and likely same fix as:

#2

Hey friends,

In the replaceIterables hook for adding ImmutableJS compatibility, there's an issue with the Immutable.Map rendering.

In React v15.6 in traverseAllChildren, there's code which prints a warning, but then says "if we're iterating over a dictionary, use entry[1] to get the value".

The result is that while there is a warning printed in dev, we still get "working" elements.

From investigating in the Immutable codebase, it appears that the way that Immutable determines whether an item is a Map-like item (a KeyedCollection) is obj["@@__IMMUTABLE_KEYED__@@"].

So for this use case, to match how React is rendering Map-like things, it seems like we would want to change the code to:

} else if (typeof obj.toJS === 'function') {
	if (obj["@@__IMMUTABLE_KEYED__@@"]) {
		obj = obj.valueSeq();
	}
	
	obj = obj.toJS();
}