Cannot read property 'download' of undefined about react-native-file-transfer HOT 3 OPEN

FileTransfer.prototype.download = function(source, target, successCallback, errorCallback, trustAllHosts, options) {
    argscheck.checkArgs('ssFF*', 'FileTransfer.download', arguments);
    var self = this;
    var subscription;

    var basicAuthHeader = getBasicAuthHeader(source);
    if (basicAuthHeader) {
        source = source.replace(getUrlCredentials(source) + '@', '');

        options = options || {};
        options.headers = options.headers || {};
        options.headers[basicAuthHeader.name] = basicAuthHeader.value;
    }

    var headers = null;
    if (options) {
        headers = options.headers || null;
    }

    if (false && headers) {
        headers = convertHeadersToArray(headers);
    }

    var win = successCallback && function(result) {
        subscription && subscription.remove();
        successCallback(result);
    };

    var fail = errorCallback && function(e) {
        subscription && subscription.remove();
        var error = new FileTransferError(e.code, e.source, e.target, e.http_status, e.body, e.exception);
        errorCallback(error);
    };

    if (this.onprogress) {
        subscription = EventEmitter.addListener('DownloadProgress-' + this._id, function(result){
            self.onprogress(newProgressEvent(result));
        });
    }

    exec(win, fail, 'FileTransfer', 'download', [source, target, trustAllHosts, this._id, headers]);
};