Base runtime code like URL, CommonJS can be shared. Even debugger support. Only difference is mainly the FFI, which is very different for Android and iOS/macOS. Shared runtimes codebase will make it easier to add more platforms as well. In future, maybe FFI code could be refactored to have a common interface which makes it easier to handle like native objects and their memory management across different FFI types (ObjC runtime, JNI).