Type Alias JsCallback 

pub type JsCallback<Args = (), Ret = ()> = Arc<ThreadsafeFunction<Args, Either<Ret, InvalidReturnValue>, Args, Status, false, true>>;

JsCallback is a type alias for a weak, caller-handled ThreadsafeFunction whose return value is validated in Rust: it represents a JavaScript function passed to the Rust side.

• Rust: JsCallback<FnArgs<(u32, f64)>, Promise<()>>
• JS: (id: number, ms: number) => Promise<void>

The Weak = true parameter means the callback does not keep its owning event loop alive, which is exactly what the host protocol needs: a worker that registered a timer or task host may exit at any time, and the runtime detects that through the threadsafe function’s aborted flag instead of pinning the worker.

Aliased Type

pub struct JsCallback<Args = (), Ret = ()> { /* private fields */ }