带接口的typehint类构造函数

interface IDownloader {
    download()
}

以及实现它的几个类:

class DownloaderA implements IDownloader {
...
}

class DownloaderB implements IDownloader {
...
}

class DownloadWorker {
    constructor(downloader: typeof DownloaderA) {
    }
}

但我不能用同样的方式输入提示:

class DownloadWorker {
    constructor(downloader: typeof IDownloader) {
    }
}

如何输入downloader参数以便传递DownloaderA和DownloaderB构造函数?