fix(connection): throw helpful error when callback param to mongoose.connect() or mongoose.createConnection() is not a function

Fix #8556

Author: vkarpov15

lib/connection.js

@@ -579,6 +579,12 @@ Connection.prototype.openUri = function(uri, options, callback) {
       '`mongoose.connect()` or `mongoose.createConnection()` is a string.');
   }
 
+  if (callback != null && typeof callback !== 'function') {
+    throw new MongooseError('3rd parameter to `mongoose.connect()` or ' +
+      '`mongoose.createConnection()` must be a function, got "' +
+      typeof callback + '"');
+  }
+
   const Promise = PromiseProvider.get();
   const _this = this;
 

lib/index.js

@@ -15,6 +15,7 @@ if (global.MONGOOSE_DRIVER_PATH) {
   require('./driver').set(require('./drivers/node-mongodb-native'));
 }
 
+const Document = require('./document');
 const Schema = require('./schema');
 const SchemaType = require('./schematype');
 const SchemaTypes = require('./schema/index');
@@ -24,7 +25,6 @@ const VALID_OPTIONS = require('./validoptions');
 const Types = require('./types');
 const Query = require('./query');
 const Model = require('./model');
-const Document = require('./document');
 const applyPlugins = require('./helpers/schema/applyPlugins');
 const get = require('./helpers/get');
 const legacyPluralize = require('mongoose-legacy-pluralize');
@@ -326,10 +326,10 @@ Mongoose.prototype.createConnection = function(uri, options, callback) {
  * @return {Promise} resolves to `this` if connection succeeded
  */
 
-Mongoose.prototype.connect = function() {
+Mongoose.prototype.connect = function(uri, options, callback) {
   const _mongoose = this instanceof Mongoose ? this : mongoose;
   const conn = _mongoose.connection;
-  return conn.openUri(arguments[0], arguments[1], arguments[2]).then(() => _mongoose);
+  return conn.openUri(uri, options, callback).then(() => _mongoose);
 };
 
 /**