You are assuming wrong, this is Blazor’s JS support library. By “default” WebAssembly has nothing outside the WASM bytecode, not even memory/allocator. It’s up to the host environment to provide the WASM module a Memory and whatever “imports” it needs.

I think you actually can't pass any non-trivial object to WASM. The only thing you can pass to and get out of WASM (IIRC) is a chunk of linear memory, a buffer. I don't think it's possible to obtain a raw pointer to an object on a JS side - passing that would be very unsafe, but also pretty much useless, unless you knew precisely the memory layout of said object. If you need to expose operations on a more complex objects to WASM, you need to encode the object identity somehow (as a number, or a buffer) and expose an API that will decode the object reference and call the needed function/method on it.