There are also exists other projects which simplify this: https://github.com/torch2424/as-bind
1. AssemblyScript functions can be exposed to Javascript via the loader utility. If the arguments are primitive types then calling them is straightforward. Complex types like strings and arrays must be converted between the JS version of the type and the AS version of the type.
2. AssemblyScript code cannot call Javascript functions or directly manipulate Javascript objects. However, Javascript objects and functions can be passed around as an opaque anyref.
Opaque anyref (externref) or reference-types WebAssembly proposal not yet in all browsers, but after it interop will become much easier. At least you don't need glue code for JS side any more.