diff --git a/models/Comment.js b/models/Comment.js
index 6fff204..9273542 100644
--- a/models/Comment.js
+++ b/models/Comment.js
@@ -1,6 +1,6 @@
 const mongoose = require('mongoose');
 
-const CommentSchema = new mongoose.Schema(
+const schema = new mongoose.Schema(
   {
     body: String,
     author: { type: mongoose.Schema.Types.ObjectId, ref: 'User' },
@@ -9,14 +9,17 @@ const CommentSchema = new mongoose.Schema(
   { timestamps: true },
 );
 
-// Requires population of author
-CommentSchema.methods.toJSONFor = function (user) {
-  return {
-    id: this._id,
-    body: this.body,
-    createdAt: this.createdAt,
-    author: this.author.toProfileJSONFor(user),
-  };
-};
+class Comment extends mongoose.Model {
+  toJSONFor(user) {
+    return {
+      id: this._id,
+      body: this.body,
+      createdAt: this.createdAt,
+      author: this.author.toProfileJSONFor(user),
+    };
+  }
+}
 
-mongoose.model('Comment', CommentSchema);
+mongoose.model(Comment, schema);
+
+module.exports = Comment;
diff --git a/models/Track.js b/models/Track.js
index b7e47d7..c27713f 100644
--- a/models/Track.js
+++ b/models/Track.js
@@ -2,7 +2,7 @@ const mongoose = require('mongoose');
 const uniqueValidator = require('mongoose-unique-validator');
 const slug = require('slug');
 
-const TrackSchema = new mongoose.Schema(
+const schema = new mongoose.Schema(
   {
     slug: { type: String, lowercase: true, unique: true },
     title: String,
@@ -18,9 +18,9 @@ const TrackSchema = new mongoose.Schema(
   { timestamps: true },
 );
 
-TrackSchema.plugin(uniqueValidator, { message: 'is already taken' });
+schema.plugin(uniqueValidator, { message: 'is already taken' });
 
-TrackSchema.pre('validate', function (next) {
+schema.pre('validate', function (next) {
   if (!this.slug) {
     this.slugify();
   }
@@ -28,38 +28,42 @@ TrackSchema.pre('validate', function (next) {
   next();
 });
 
-TrackSchema.methods.slugify = function () {
-  this.slug = slug(this.title) + '-' + ((Math.random() * Math.pow(36, 6)) | 0).toString(36);
-};
-
-TrackSchema.methods.isVisibleTo = function (user) {
-  if (this.visible) {
-    return true;
+class Track extends mongoose.Model {
+  slugify() {
+    this.slug = slug(this.title) + '-' + ((Math.random() * Math.pow(36, 6)) | 0).toString(36);
   }
 
-  if (!user) {
+  isVisibleTo(user) {
+    if (this.visible) {
+      return true;
+    }
+
+    if (!user) {
+      return false;
+    }
+
+    if (user._id.toString() === this.author._id.toString()) {
+      return true;
+    }
+
     return false;
   }
 
-  if (user._id.toString() === this.author._id.toString()) {
-    return true;
+  toJSONFor(user, include) {
+    return {
+      slug: this.slug,
+      title: this.title,
+      description: this.description,
+      createdAt: this.createdAt,
+      updatedAt: this.updatedAt,
+      visibleForAll: this.author ? this.author.areTracksVisibleForAll : false,
+      visible: this.visible,
+      author: this.author.toProfileJSONFor(user),
+      ...(include && include.body ? { body: this.body } : {}),
+    };
   }
+}
 
-  return false;
-};
+mongoose.model(Track, schema);
 
-TrackSchema.methods.toJSONFor = function (user, include) {
-  return {
-    slug: this.slug,
-    title: this.title,
-    description: this.description,
-    createdAt: this.createdAt,
-    updatedAt: this.updatedAt,
-    visibleForAll: this.author ? this.author.areTracksVisibleForAll : false,
-    visible: this.visible,
-    author: this.author.toProfileJSONFor(user),
-    ...(include && include.body ? { body: this.body } : {}),
-  };
-};
-
-mongoose.model('Track', TrackSchema);
+module.exports = Track;
diff --git a/models/TrackData.js b/models/TrackData.js
index 670212b..f084287 100644
--- a/models/TrackData.js
+++ b/models/TrackData.js
@@ -2,7 +2,7 @@ const mongoose = require('mongoose');
 const uniqueValidator = require('mongoose-unique-validator');
 const slug = require('slug');
 
-const TrackDataSchema = new mongoose.Schema(
+const schema = new mongoose.Schema(
   {
     slug: { type: String, lowercase: true, unique: true },
     points: [
@@ -23,17 +23,21 @@ const TrackDataSchema = new mongoose.Schema(
   { timestamps: true },
 );
 
-TrackDataSchema.plugin(uniqueValidator, { message: 'is already taken' });
+schema.plugin(uniqueValidator, { message: 'is already taken' });
 
-TrackDataSchema.pre('validate', function (next) {
+schema.pre('validate', function (next) {
   if (!this.slug) {
     this.slugify();
   }
   next();
 });
 
-TrackDataSchema.methods.slugify = function () {
-  this.slug = slug('td') + '-' + ((Math.random() * Math.pow(36, 6)) | 0).toString(36);
-};
+class TrackData extends mongoose.Model {
+  slugify() {
+    this.slug = 'td-' + String((Math.random() * Math.pow(36, 6)) | 0).toString(36);
+  }
+}
 
-mongoose.model('TrackData', TrackDataSchema);
+mongoose.model(TrackData, schema);
+
+module.exports = TrackData;
diff --git a/models/User.js b/models/User.js
index 2b77e6d..d8b4fde 100644
--- a/models/User.js
+++ b/models/User.js
@@ -4,7 +4,7 @@ const crypto = require('crypto');
 const jwt = require('jsonwebtoken');
 const secret = require('../config').secret;
 
-const UserSchema = new mongoose.Schema(
+const schema = new mongoose.Schema(
   {
     username: {
       type: String,
@@ -39,96 +39,88 @@ const UserSchema = new mongoose.Schema(
   { timestamps: true },
 );
 
-UserSchema.plugin(uniqueValidator, { message: 'ist bereits vergeben. Sorry!' });
+schema.plugin(uniqueValidator, { message: 'ist bereits vergeben. Sorry!' });
 
-UserSchema.methods.validPassword = function (password) {
-  const hash = crypto.pbkdf2Sync(password, this.salt, 10000, 512, 'sha512').toString('hex');
-  return this.hash === hash;
-};
+class User extends mongoose.Model {
+  validPassword(password) {
+    const hash = crypto.pbkdf2Sync(password, this.salt, 10000, 512, 'sha512').toString('hex');
+    return this.hash === hash;
+  }
 
-UserSchema.methods.setPassword = function (password) {
-  this.salt = crypto.randomBytes(16).toString('hex');
-  this.hash = crypto.pbkdf2Sync(password, this.salt, 10000, 512, 'sha512').toString('hex');
-};
+  setPassword(password) {
+    this.salt = crypto.randomBytes(16).toString('hex');
+    this.hash = crypto.pbkdf2Sync(password, this.salt, 10000, 512, 'sha512').toString('hex');
+  }
 
-UserSchema.methods.generateJWT = function () {
-  const today = new Date();
-  const exp = new Date(today);
-  exp.setDate(today.getDate() + 60);
+  generateJWT() {
+    const today = new Date();
+    const exp = new Date(today);
+    exp.setDate(today.getDate() + 60);
 
-  return jwt.sign(
-    {
-      id: this._id,
+    return jwt.sign(
+      {
+        id: this._id,
+        username: this.username,
+        exp: parseInt(exp.getTime() / 1000),
+      },
+      secret,
+    );
+  }
+
+  toAuthJSON() {
+    return {
       username: this.username,
-      exp: parseInt(exp.getTime() / 1000),
-    },
-    secret,
-  );
-};
-
-UserSchema.methods.toAuthJSON = function () {
-  return {
-    username: this.username,
-    email: this.email,
-    token: this.generateJWT(),
-    bio: this.bio,
-    image: this.image,
-    areTracksVisibleForAll: this.areTracksVisibleForAll,
-    apiKey: this._id,
-  };
-};
-
-UserSchema.methods.toProfileJSONFor = function (user) {
-  return {
-    username: this.username,
-    bio: this.bio,
-    image: this.image || 'https://static.productionready.io/images/smiley-cyrus.jpg',
-    following: user ? user.isFollowing(this._id) : false,
-  };
-};
-
-UserSchema.methods.favorite = function (id) {
-  if (this.favorites.indexOf(id) === -1) {
-    this.favorites.push(id);
+      email: this.email,
+      token: this.generateJWT(),
+      bio: this.bio,
+      image: this.image,
+      areTracksVisibleForAll: this.areTracksVisibleForAll,
+      apiKey: this._id,
+    };
   }
 
-  return this.save();
-};
-
-UserSchema.methods.unfavorite = function (id) {
-  this.favorites.remove(id);
-  return this.save();
-};
-
-UserSchema.methods.isFavorite = function (id) {
-  return this.favorites.some(function (favoriteId) {
-    return favoriteId.toString() === id.toString();
-  });
-};
-
-UserSchema.methods.isTrackVisible = function (id) {
-  return this.areTracksVisibleForAll();
-};
-
-UserSchema.methods.follow = function (id) {
-  if (this.following.indexOf(id) === -1) {
-    this.following.push(id);
+  toProfileJSONFor(user) {
+    return {
+      username: this.username,
+      bio: this.bio,
+      image: this.image || 'https://static.productionready.io/images/smiley-cyrus.jpg',
+      following: user ? user.isFollowing(this._id) : false,
+    };
   }
 
-  return this.save();
-};
+  async favorite(id) {
+    if (this.favorites.indexOf(id) === -1) {
+      this.favorites.push(id);
+    }
 
-UserSchema.methods.unfollow = function (id) {
-  this.following.remove(id);
-  return this.save();
-};
+    return await this.save();
+  }
 
-UserSchema.methods.isFollowing = function (id) {
-  return this.following.some(function (followId) {
-    return followId.toString() === id.toString();
-  });
-};
+  async unfavorite(id) {
+    this.favorites.remove(id);
+    return await this.save();
+  }
 
-mongoose.model('User', UserSchema);
+  follow(id) {
+    if (this.following.indexOf(id) === -1) {
+      this.following.push(id);
+    }
 
-module.exports = mongoose.model('User');
+    return this.save();
+  }
+
+  unfollow(id) {
+    this.following.remove(id);
+    return this.save();
+  }
+
+  isFollowing(id) {
+    return this.following.some(function (followId) {
+      return followId.toString() === id.toString();
+    });
+  }
+}
+
+mongoose.model(User, schema);
+
+module.exports = User;