How does dynamic object access work in V8?

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I was surprised to find out that JavaScript objects are not in fact hash maps under the hood, instead they are more similar to structs. From what I understand, getting and setting properties on an object is fast because the memory location of the value is at a fixed offset, as it would be in a struct or a class. What I don’t understand is how the syntax maps to that fixed offset. Ie what happens when the compiler sees obj.a or obj[‘a’]. Is that syntax transformed into an integer offset at run time or compile time or JIT? I guess what I’m trying to understand is how can it transform the incoming string ‘a’ into an integer index efficiently without doing something like index = hash(‘a’) % objectLength.

Maybe the gap in my knowledge is I don’t fully get how structs work.

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