use nodejs, express and MongoDB to do a set of services, but the response time of the interface is very long. The
test removes the query database and finds that the response time is reduced to 1200 milliseconds.
the following is my code, ask for advice

var express = require("express");
var fs = require("fs");
var path = require("path");
var crypto = require("crypto"); //
var redis = require("redis");   // Redis
var router = express.Router();
var MongoClient = require("mongodb").MongoClient;
var ObjectID = require("mongodb").ObjectID;
var url = "mongodb://localhost:27017/books";
// 
var buf = new Buffer.alloc(2048);
var client = redis.createClient(6379, "localhost", {});

// 
function encrypt(pw){
    var key = Math.random().toString().substring(2);
    pw = pw + key;
    var md5 = crypto.createHash("md5");
    var r = md5.update(pw).digest("hex");
    return {key: key, pw: r}
}

client.on("ready", function(err){
    if(err) throw err
    console.log("redis ready")
});

// app
router.post("/enroll", function(req, res){
    var data = {
        userName: req.body.userName,
        sex: req.body.sex,
        userPhone: req.body.userPhone,
        userEmail: req.body.userEmail,
        password: req.body.password,
        status: 1
    }
    for(var k in data){
        if(!data[k]){
            res.json({code:4, content:""});
            return false
        }
    }
    MongoClient.connect(url, { useNewUrlParser: true }, function(err, db) {
        if (err) throw err;
        var dbo = db.db("books");
        dbo.collection("user").find({userPhone: data.userPhone}).count(function(err, num){
            if(err) throw err;
            if(num == 0){
                // 
                var pwObj = encrypt(data.password);
                data.password = pwObj.pw;
                data.key = pwObj.key;
                dbo.collection("user").insertOne(data, function(err, result) {
                    if (err){
                        res.json({code:4, content: ""});
                        throw err;
                    }
                    res.json({code:1, content: ""});
                })
            }else{
                res.json({code:2, content: ""})
            }
            db.close();
        });
    });
});

// APP
router.post("/login", function(req, res){
    var userPhone = req.body.userPhone;
    var password = req.body.password;
    if(userPhone && password){
        MongoClient.connect(url, { useNewUrlParser: true }, function(err, db) {
            if (err) throw err;
            var dbo = db.db("books");
            dbo.collection("user").find({userPhone: userPhone}).toArray(function(err, resArr) {
                if (err) throw err;
                if(resArr.length>0){
                    password = password + resArr[0].key;
                    var md5 = crypto.createHash("md5");
                    var r = md5.update(password).digest("hex");
                    if(r == resArr[0].password){
                        res.json({code: 1, content: resArr[0]._id});
                    }else{
                        res.json({code: 2, content: ""});
                    }
                }else{
                    res.json({code: 2, content: ""});
                }
                db.close();
            });
        });
    }else{
        res.json({code: 4, content: ""});
    }
});

// 
router.post("/findUserById", function(req, res){
    var userInfoId = req.body.userInfoId;
    if(!userInfoId){
        res.json({code:4, content: ""});
        return false;
    }
    MongoClient.connect(url, { useNewUrlParser: true }, function(err, db) {
        if (err) throw err;
        var dbo = db.db("books");
        dbo.collection("user").find({_id: ObjectID(userInfoId)}).toArray(function(err, result) {
            if (err) throw err;
            res.json({code:1, content:result[0]});
            db.close();
        });
    });
});

// 
router.post("/findBooksOfPage", function(req, res){
    var dataNumber = req.body.dataNumber;
    var keyWord = req.body.keyWord;
    var data = {
        status: "1"
    }
    if(req.body.classes != "0"){
        data.classes = req.body.classes
    }
    if(keyWord){
        data.$or = [
            {bookName: new RegExp(keyWord)},
            {author: new RegExp(keyWord)}
        ]
    }
    MongoClient.connect(url, { useNewUrlParser: true }, function(err, db) {
        if (err) throw err;
        var dbo = db.db("books");
        dbo.collection("book").find(data).skip(dataNumber).limit(10).toArray(function(err, result) {
            if (err) throw err;
            res.json({code:1, content:result});
            db.close();
        });
    });
});

// 
router.post("/findBookById", function(req, res){
    var id = req.body.bookInfoId;
    MongoClient.connect(url, { useNewUrlParser: true }, function(err, db) {
        if (err) throw err;
        var dbo = db.db("books");
        dbo.collection("book").find({_id: ObjectID(id)}).toArray(function(err, result) {
            if (err) throw err;
            res.json({code:1, content:result[0]});
            db.close();
        });
    });
});

// 
router.post("/findBookshelfOfPage", function(req, res){
    var userInfoId = req.body.userInfoId;
    var dataNumber = req.body.dataNumber;
    MongoClient.connect(url, { useNewUrlParser: true }, function(err, db) {
        if (err) throw err;
        var dbo = db.db("books");
        dbo.collection("bookshelf").find({userInfoId: userInfoId}).skip(dataNumber).limit(10).toArray(function(err, result) {
            if (err) throw err;
            res.json({code:1, content:result});
            db.close();
        });
    });
});

// 
router.post("/addToBookshelf", function(req, res){
    var data = {
        userInfoId: req.body.userInfoId,
        bookInfoId: req.body.bookInfoId,
        bookName: req.body.bookName,
        author: req.body.author,
        bookImg: req.body.bookImg,
        bookSize: req.body.bookSize,
        location: "0"
    }
    for(var k in data){
        if(k != "location" && !data[k]){
            res.json({code:4, content: ""});
            return false;
        }
    }
    MongoClient.connect(url, { useNewUrlParser: true }, function(err, db) {
        if (err) throw err;
        var dbo = db.db("books");
        dbo.collection("bookshelf").find({userInfoId: data.userInfoId, bookInfoId: data.bookInfoId}).toArray(function(err, result) {
            if (err) throw err;
            if(result.length>0){
                res.json({code:2, content: ""});
            }else{
                dbo.collection("bookshelf").insertOne(data, function(err, result){
                    if (err) throw err;
                    res.json({code:1, content:""});
                })
            }
            db.close();
        });
    });
});

// 
router.get("/downloadImg", function(req, res){
    var img = req.query.fileName;
    if(!img){return}
    var url = path.resolve(__dirname, "../public/scratch_file/", img);
    try{
        fs.accessSync(url);
        res.sendFile(url);
    }catch(e){
        url = path.resolve(__dirname, "../public/books_img/", img);
        res.sendFile(url);
    }
});

// 
router.post("/delBookshelf", function(req, res){
    var bookInfoId = req.body.bookInfoId;
    var userInfoId = req.body.userInfoId;
    MongoClient.connect(url, { useNewUrlParser: true }, function(err, db) {
        if (err){
            res.json({code:4, content: ""});
            throw err;
        }
        var dbo = db.db("books");
        dbo.collection("bookshelf").deleteOne({userInfoId:userInfoId,bookInfoId: bookInfoId}, function(err, result) {
            if (err){
                res.json({code:4, content: ""});
                throw err;
            }
            res.json({code:1, content: ""});
            db.close();
        });
    });
});

// 
router.post("/findBookshelfById", function(req, res){
    var bookInfoId = req.body.bookInfoId;
    var userInfoId = req.body.userInfoId;
    MongoClient.connect(url, { useNewUrlParser: true }, function(err, db) {
        if (err){
            res.json({code:4, content: ""});
            throw err;
        }
        var dbo = db.db("books");
        dbo.collection("bookshelf").find({userInfoId:userInfoId,bookInfoId: bookInfoId}).toArray(function(err, result) {
            if (err){
                res.json({code:4, content: ""});
                throw err;
            }
            res.json({code:1, content: result});
            db.close();
        });
    });
});

// 
router.post("/findBookOfPage", function(req, res){
    var userInfoId = req.body.userInfoId;
    var bookInfoId = req.body.bookInfoId;
    var location = req.body.location;
    if(!bookInfoId && !location){
        res.json({code:4, content: ""});
        return false
    }
    MongoClient.connect(url, { useNewUrlParser: true }, function(err, db) {
        var dbo = db.db("books");
        dbo.collection("book").find({_id: ObjectID(bookInfoId)}).toArray(function(err, result) {
            if (err) throw err;
            if(result[0].bookUrl){
                var bookUrl = "./public/books_txt/"+result[0].bookUrl;
                fs.open(bookUrl, "r", function (err, fd) {
                    if (err) throw err;
                    // 
                    fs.read(fd, buf, 0, buf.length, location, function (err, bytes) {
                        if (err) throw err;
                
                        // 
                        if (bytes > 0) {
                            res.json({code:1, content: buf.slice(0, bytes).toString()});
                        }else{
                            res.json({code:2, content: ""});
                        }
                
                        // 
                        fs.close(fd, function (err) {
                            if (err) throw err;
                        })
                    })
                })
            }else{
                res.json({code:4, content: ""});
            }
            
        });
        var whereStr = {userInfoId: userInfoId,bookInfoId: bookInfoId};  // 
        var updateStr = {$set: { location: location }};
        dbo.collection("bookshelf").updateOne(whereStr, updateStr, function(err, result) {
            if (err) throw err;
        });
        db.close();
    });
});

// MongoClient.connect(url, { useNewUrlParser: true }, function(err, db) {
//     var dbo = db.db("books");
//     // 
//     // dbo.collection("bookshelf").deleteOne({"_id": ObjectID("5c384e1460e7462390755a67")}, function(err, result) {
//     //     if (err) throw err;
//     // });
//     // 
//     dbo.collection("bookshelf").find().toArray(function(err, result) {
//         if (err) throw err;
//         console.log(result);
//     });

//     db.close();
// });

module.exports = router;