Implement `[LegacyFactoryFunction]`#213

Open

ExE-Boss wants to merge 2 commits intojsdom:mainfrom

ExE-Boss:feat/ext-attr/legacy-factory-function

Commits on Mar 20, 2021

Implement [LegacyFactoryFunction]
ExE-Boss
committed

Commits on Mar 23, 2021

Fix order of `Impl.legacyFactoryFunction` and `Impl.init` calls
ExE-Boss
committed