The use of that piece of code is explained in the comment directly above it.

Originally posted by @LinusBorg in https://github.com/vuejs/vue-next/issues/2951#issuecomment-755188957

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i think the code above i mentinoned is useless, because in function createReactiveObject will solve the situation that if trying to observe a readonly proxy, return the readonly version, becasuse in createReactiveObject , except readonly() on a reactive object, as long as the target is a proxy, the function createReactiveObject will return the target, so the code is repleat, and when i delete the code above i mentioned, when i run 'npm test', it can pass and has no errors

Hello, thank you for taking time filling this issue!

However, we kindly ask you to use our Issue Helper when creating new issues, in order to ensure every issue provides the necessary information for us to investigate. This explains why your issue has been automatically closed by me (your robot friend!).

I hope to see your helper-created issue very soon!

i do not find a bug, i find some code is useless and want to delete