login with email or username with MongoDB in Node.js

I am wondering if there is a way to let user to login with both username or email I searched a lot of times for but doesn't found a working method. I don't have a single idea how to do this, please help with the easiest way if possible. here is what my user schema looks like :

var mongoose = require("mongoose");
var passportLocalMongoose = require("passport-local-mongoose");

var UserSchema = new mongoose.Schema({
    fullname: String,
    username: { type : String , lowercase : true , unique: true ,  required: true, minlength: 3, maxlength: 10},
    email: String, 
    password: String,
    mobile: String,
    gender: String,
    profession: String,
    city: String,
    country: String,
    joining: {type: Date, default: Date.now}
});

UserSchema.plugin(passportLocalMongoose);

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

Addition info: I am working on top of nodejs. Any help is seriously appreciated. thnx

 //the simple example of login// 
 router.post('/users/login', function(req, res) {
     var users = req.app;
     var email = req.body.email;
     var password = req.body.password;
     var username = req.body.username;
     var data;
     if (email.length > 0 && password.length > 0) {
         data = {
             email: email,
             password: password
         };
     }
     else if(username.length > 0 && password.length > 0) {
         data = {
             username: username,
             password: password
         };
     } else {
         res.json({
             status: 0,
             message: err
         });
     }
     users.findOne(data, function(err, user) {
         if (err) {
             res.json({
                 status: 0,
                 message: err
             });
         }
         if (!user) {
             res.json({
                 status: 0,
                 msg: "not found"
             });
         }
         res.json({
             status: 1,
             id: user._id,
             message: " success"
         });
     })
 } else {
     res.json({
         status: 0,
         msg: "Invalid Fields"
     });
 }
 });

 //and if you have to create schema 

 var db_schema = new Schema({
     email: {
         type: String,
         required: true,
         unique: true
     },
     password: {
         type: String,
         required: true,
         unique: true
     },
 });
 // define this in your db.js
 var login_db = mongoose.model('your_db_name', db_schema);
 return function(req, res, next) {
     req.app = login_db;
     next();
 };