我想用GridJS上传图片。我使用https://www.npmjs.org/package/gridfs-stream。它给我errorReferenceError: ObjectID is not defined。
我是这方面的初学者，所以不知道发生了什么。
如何解决此错误？

var Grid = require('gridfs-stream');
    var conn = mongoose.createConnection('localhost', 'Test', 27017);
    var gfs = Grid(conn.db, mongoose);

    var fileId = new ObjectID(uniqId);
    var fileType = req.header('X-File-Type');
    var fileName = req.header('X-File-Name');
    var uniqId = req.param('uniqId', '112211112111');

    console.log('upload start');
    // streaming to gridfs
    var writestream = gfs.createWriteStream(fileId, [{ "content_type": fileType, "metadata": { "fileName": fileName, "uploaded_at": (new Date()).toString() } }]);
    fs.createReadStream('/some/path').pipe(writestream);

    // streaming from gridfs
    var readstream = gfs.createReadStream(fileId, [{ "content_type": fileType, "metadata": { "fileName": fileName, "uploaded_at": (new Date()).toString() } }]);

    //error handling, e.g. file does not exist
    readstream.on('error', function (err) {
        console.log('An error occurred!', err);
        throw err;
    });

    readstream.pipe(response);
    console.log('upload done');