What is the relationship between javascript virtual machine and WebAssembly abstract machine?
As I know that WebAssembly directly using javascript virtual machine instead of building a new vm. But I see "WebAssembly abstract machine" on the official website, so what is the relationship between these two stuffs?
A JavaScript "virtual machine" is an implementation detail of practical implementations, nothing that is defined by the language.
The WebAssembly "abstract machine" is a specification device to define the semantics of Wasm execution. It isn't an implementation but a formal concept.
At least in browsers, Wasm and JS are implemented as part of a single VM. However, standalone implementations of Wasm exist as well.