报错DeprecationWarning: collection.count is deprecated, and will be removed in a future version

nodejs操作mongodb 用db.collection(collectionName).count(json)报错 如下： nodejs操作mongodb报错 (node:664) DeprecationWarning: collection.count is deprecated, and will be removed in a future version. Use collection.countDocuments or collection.estimatedDocumentCount instead

  //统计数量的方法
    count(collectionName,json){

        return new  Promise((resolve,reject)=> {
            this.connect().then((db)=> {

                var result = db.collection(collectionName).count(json);
                result.then(function (count) {

                        resolve(count);
                    }
                )
            })
        })

    }