自己實現了一個縮水版的EventTarget：interface MyEventTarget {    addEventListener: (type: string, listener: EventListener) => void}但如果想和原生EventTarget混合使用的話：function test(foo: MyEventTarget | EventTarget) {    return foo.addEventListener('click', console.log);}會報錯：無法調用類型缺少調用簽名的表達式。類型“((type: string, listener: EventListener) => void) | ((type: string, listener: EventListener | Eve...”沒有兼容的調用簽名。如果強行拆開的話，卻又可以：function test(foo: MyEventTarget | EventTarget) {    if (foo instanceof EventTarget) {        return foo.addEventListener('click', console.log);    }    else {        return foo.addEventListener('click', console.log);    }}// OK但是實在是太丑了。所以請問一下大家：Is it a feature, or a bug?不論是feature還是bug，類似的情形應該怎樣優雅地處理？