Gio.File.prototype.query_default_handler

function query_default_handler(cancellable: Gio.Cancellable): Gio.AppInfo {
    // Gjs wrapper for g_file_query_default_handler()
}

Returns the Gio.AppInfo that is registered as the default application to handle the file specified by file.

If cancellable is not null, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error Gio.IOErrorEnum.cancelled will be returned.

cancellable: optional Gio.Cancellable object, null to ignore
Returns: a Gio.AppInfo if the handle was found, null if there were errors. When you are done with it, release it with GObject.Object.prototype.unref