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Magento 2: Are uiClass/uiElement Imports/Exports order sensitive?
The answer is mostly no. Imports/Exports values are fetched via the
uiRegistry.get’s asynchronous callback method which means if the imports or exports attempts to access an item that doesn’t exist yet in the registry, the system will “wait” until the item does exist. So they’ll always have a value, if it exists, although the possibility of other processes manipulating an items after the get callback fires does exist.
It’s like they all saw us celebrating javascript’s thread-less universe and said “no, you must still suffer the concurrency monster”.