TypeError：user.comparePassword不是express js中的函数

Question

显示错误：

TypeError: user.comparePassword is not a function
    at User.findOne (/home/ubuntu/work/training/git new/eventica/controller/login.js:59:13)
    at /home/ubuntu/work/training/git new/eventica/node_modules/mongoose/lib/model.js:4846:16
    at /home/ubuntu/work/training/git new/eventica/node_modules/mongoose/lib/query.js:4283:12
    at process.nextTick (/home/ubuntu/work/training/git new/eventica/node_modules/mongoose/lib/query.js:2776:28)
    at _combinedTickCallback (internal/process/next_tick.js:131:7)
    at process._tickCallback (internal/process/next_tick.js:180:9)

我的问题在哪里？

我的JavaScript文件：

const User = require('../models/User.js');
var funcs = require('../functions');

var config = require('config');
Web3 = require('web3')

web3 = new Web3(new Web3.providers.HttpProvider(config.get('ethereum.host')));
const fs = require("fs");
const path = require('path');

module.exports = function (app) {


  app.get('/signin', function (req, res) {

      res.render('signin', {
               pageTitle: 'Welcome - ' ,
                  layout: false             
           });
     //res.redirect('/signin');
  });


  app.get('/signup', function (req, res) {

    res.render('signup', {
      pageTitle: 'Welcome - ',
      layout: false
    });
  });



  app.post("/signin", function (req, res) {
    sess = req.session;
    var email = req.body.email;
    var password = req.body.password;

    const userData = {
      email: email.trim(),
      password: password.trim()
    };

    // find a user by email address
    User.findOne({ email: userData.email }, (err, user) => {
      //console.log ("user...", user);

      if (err) { throw err; }

      if (!user) {
        return res.json({
          status: 'Error',
          msg: 'User details is not found for this email, please register....'
        });
      }

      // check if a hashed user's password is equal to a value saved in the database
       user.comparePassword(userData.password, (passwordErr, isMatch) => {
         if (err) { throw err; }

        if (!isMatch) {
          return res.json({
            status: 'Error',
            msg: 'Incorrect email or password, please try again..'
          });

          //req.flash('error', 'Incorrect email or password, please try again..');
          //return res.redirect('/login');
          // const error = new Error('Incorrect email or password');
          // error.name = 'IncorrectCredentialsError';
          // console.log("Password doesnt match...")
          //res.json(error);
        } else {


          sess.user = user;
          return res.json({
            status: 'OK',
            msg: 'Login successful'
          });

        } 

        //  return res.json({
        //    status:'OK',
        //    msg:'Login successfully'
        // });

         // res.redirect("/eventica");

      });
    });
  });

模型/User.js

module.exports = mongoose.model('User', UserSchema);


UserSchema.methods.comparePassword = function comparePassword(password, callback) {
    bcrypt.compare(password, this.password, callback);
};


// UserSchema.pre('save', function (next) {
//     const user = this;

    UserSchema.pre('save', function saveHook(next) {
        const user = this;

        // proceed further only if the password is modified or the user is new
        if (!user.isModified('password')) return next();


        return bcrypt.genSalt((saltError, salt) => {
            if (saltError) { return next(saltError); }

            return bcrypt.hash(user.password, salt, (hashError, hash) => {
                if (hashError) { return next(hashError); }

                // replace a password string with hash value
                user.password = hash;

                return next();
            });
        });
    });