JavaScript-defined standalone WinRT interfaces

This sample implements IBackgroundTask, IStringable, and IClosable on one standalone native object. A second implemented object supplies a controlled IBackgroundTaskInstance. Calling the generated task.run(instance) enters the native WinRT vtable, invokes the JavaScript handler, and makes nested native property calls on the task instance.

There is no WinUI base, package identity, OS task registration, COM server, or background activation. Unused task-instance fixture methods throw rather than pretending that an OS registration or deferral exists.

From the repository root, build the matching runtime and generator:

cargo build -p dynwinrt-codegen
Push-Location .\bindings\js
npm ci
npm run build
Pop-Location

Push-Location .\samples\js\interface-implementation
npm install --ignore-scripts --omit=optional
.\generate.ps1 -Codegen ..\..\..\target\debug\dynwinrt-codegen.exe
npm start
Pop-Location

The local npm dependency uses the runtime built in this checkout. Generation auto-detects the Windows SDK; pass -Winmd to select another Windows.winmd.

The factory returns a management handle. impl.value is the stable primary interface; use try/finally with impl.dispose() for the common pattern. interfaces: [[Interface, handlers], ...] adds explicitly typed interfaces. The handle owns and releases its primary view; no releaseProjected(impl.value) is needed.

The handle and advanced independent views have separate references. impl.release() releases only the creator's reference, so the retained views continue to work. impl.dispose() disconnects all future callbacks; the sample confirms a later native call fails and prints its contextual diagnostic. An already entered callback is allowed to finish. IClosable.Close is just another handler-defined method, not a hidden alias for owner disposal. The generated package's releaseProjected(view) independently releases each typed view.

See the public guide for the supported contracts and owner-thread/lifetime restrictions.