使用jquery从mongodb中检索数据到变量中

Question

我有这个代码检查是否已经使用了用户名（存储在json文件中）现在它从json文件中获取数据。我怎么能这样做，但从mongodb集合中获取数据？有可能吗？

提前致谢。

var userList;
$.getJSON("/usernames.json", function(data) {
      userList=data.map(function(user){ return user.username});
})

function validateUserList() {
      return $.inArray($('#username').val(), userList) > -1

}

$(function() {
      $(':input[name=username]').blur(function() {

            if (!validateUserList()) {

                  $('div#validUser').text('');
            } else {

                  $('div#validUser').text('Username is already taken.');
                }

      });
});

这是注册用户的Node.js代码

我将数据保存到2个不同的集合中，I.d喜欢只从用户名集合中获取数据。

// Register Proccess
router.post('/register', upload.single('avatar'), function(req, res){


  const username  = req.body.username;
  const email     = req.body.email;
  const password  = req.body.password;
  const password2 = req.body.password2;
  const date      = new Date();


  if(req.file){
    var avatar    = req.file.filename;
  } else {
    var avatar    = 'noimage.png';
  }

  // check to make sure this user hasnt registered
var testThisName = username;
var queryforUsername = {};
queryforUsername["username"] = testThisName;

Username.find(queryforUsername, function(error,item) {
    if(error) throw error;
    if(item.length > 0) {
      req.flash('warning', 'That username is already taken!')
      res.redirect('/users/register');
    } else if (item.length == 0) {

  req.checkBody('username', 'Username is required').notEmpty();
  req.checkBody('email', 'Email is required').notEmpty();
  req.checkBody('email', 'Email is not valid').isEmail();
  req.checkBody('password', 'Password is required').notEmpty();
  req.checkBody('password2', 'Passwords do not match').equals(req.body.password);

  let {errors, validationResults} = require('express-validator');

  if(errors){
    res.render('register', {
      errors:errors
    });

  } else{

    let newUser = new User({
      username:username,
      email:email,
      password:password,
      date: date,
      avatar: avatar
    });

    let newUsername = new Username({
      username:username,

    });

    bcrypt.genSalt(10, function(err, salt){
      bcrypt.hash(newUser.password, salt, function(err, hash){
        if(err){
          console.log(err);
        }
        newUser.password = hash;
        newUser.save(function(err){
          if(err){
            console.log(err);
            return;
          } else {
            req.flash('success','You are now registered and can log in');
            res.redirect('/');
          }
        });
        newUsername.save(function(err){
          if(err){
            console.log(err);
            return;
          }
        });
      });
    });
  }
  }
  })
});