Just because a language is specified different to C/C++ doesn't make it quirky. All of your example are just showing the specified behavior of any flavour of modern ECMAscript.
I would only consider this a quirk if the standard operators suddenly changed the specified behavior to handle typed arrays differently, i.e. if you assigned the result to another field of a Uint8Array and the results would differ or if assignments to untyped variables suddenly exposed the same overflow as the typed array ones.
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Just because a language is specified different to C/C++ doesn't make it quirky. All of your example are just showing the specified behavior of any flavour of modern ECMAscript.
I would only consider this a quirk if the standard operators suddenly changed the specified behavior to handle typed arrays differently, i.e. if you assigned the result to another field of a Uint8Array and the results would differ or if assignments to untyped variables suddenly exposed the same overflow as the typed array ones.