`StubArray` workaround is incompatible with terser's `unsafe_arrows` option about mobx HOT 4 OPEN

This workaround is not fixable I think as the arrow functions cannot act as base classes. The reason this downlevels this way is IIRC because when proxies are not used, this was the only way to reasonably correct inherit from the built-in array. If LegacyArray extends Array works nowadays, happy approve a PR for that!

I know it was a limitation in the past, and disabling proxies and using legacy array in the first place, is probably to target something from the past :) (Will be removed in next major)

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Do you have an idea for workaround?

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It's hard to say. TBH I'm not exactly sure why this workaround even exists!
I can see it was added in a9b5ed2 but the commit has no attached PR nor does it have any useful commit message.

In that commit I can see that there used to be some code that mutated the prototype - but that code is long since gone -- in v6 from the looks of it based on this comment:

Seems to me like this code could just be class LegacyObservableArray<T> extends Array?

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It also seems odd to me that MobX's build process downlevels classes to functions since all browser have had support since around 2016.

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