SWI-Prolog -- is

Documentation
- Reference manual
  - Using SWI-Prolog in your browser (WASM)
    - Accessing JavaScript from Prolog
      - Asynchronous access to JavaScript from Prolog
        
        await/2
        
        is_async/0
- Packages

[semidet]is_async

True when we can call await/2 in the current state. This implies Prolog has been called from JavaScript code that is prepared to deal with Prolog yielding and Prolog is not inside a callback from C (WASM).