refactor: use driver.js singleton rather than global.$MongooseDriver

Re: #6705

Author: vkarpov15

.eslintignore

@@ -5,3 +5,4 @@ test/model.discriminator.test.js
 tools/
 test/es6/
 test/files/
+dist/

lib/browser.js

@@ -1,6 +1,6 @@
 /* eslint-env browser */
 
-global.$MongooseDriver = require('./drivers/browser');
+require('./driver').set(require('./drivers/browser'));
 
 var DocumentProvider = require('./document_provider.js');
 var PromiseProvider = require('./promise_provider');

lib/connection.js

@@ -6,7 +6,7 @@
 
 const EventEmitter = require('events').EventEmitter;
 const Schema = require('./schema');
-const Collection = global.$MongooseDriver.Collection;
+const Collection = require('./driver').get().Collection;
 const STATES = require('./connectionstate');
 const MongooseError = require('./error');
 const PromiseProvider = require('./promise_provider');

lib/driver.js

@@ -0,0 +1,15 @@
+'use strict';
+
+/*!
+ * ignore
+ */
+
+let driver = null;
+
+module.exports.get = function() {
+  return driver;
+};
+
+module.exports.set = function(v) {
+  driver = v;
+};

lib/index.js

@@ -4,7 +4,9 @@
  * Module dependencies.
  */
 
-global.$MongooseDriver = require(global.MONGOOSE_DRIVER_PATH || './drivers/node-mongodb-native');
+const driverPath = global.MONGOOSE_DRIVER_PATH ||
+  './drivers/node-mongodb-native';
+require('./driver').set(require(driverPath));
 
 const Schema = require('./schema');
 const SchemaType = require('./schematype');

lib/query.js

@@ -7,7 +7,7 @@
 const CastError = require('./error/cast');
 const ObjectParameterError = require('./error/objectParameter');
 const QueryCursor = require('./cursor/QueryCursor');
-const ReadPreference = global.$MongooseDriver.ReadPreference;
+const ReadPreference = require('./driver').get().ReadPreference;
 const applyWriteConcern = require('./helpers/schema/applyWriteConcern');
 const cast = require('./cast');
 const castUpdate = require('./helpers/query/castUpdate');

lib/schema.js

@@ -11,7 +11,7 @@ const VirtualType = require('./virtualtype');
 const get = require('lodash.get');
 const getIndexes = require('./helpers/schema/getIndexes');
 const mpath = require('mpath');
-const readPref = global.$MongooseDriver.ReadPreference;
+const readPref = require('./driver').get().ReadPreference;
 const utils = require('./utils');
 
 let MongooseTypes;

lib/types/buffer.js

@@ -2,7 +2,7 @@
  * Module dependencies.
  */
 
-var Binary = global.$MongooseDriver.Binary;
+var Binary = require('../driver').get().Binary;
 var utils = require('../utils');
 
 /**

lib/types/decimal128.js

@@ -8,4 +8,4 @@
  * @constructor ObjectId
  */
 
-module.exports = global.$MongooseDriver.Decimal128;
+module.exports = require('../driver').get().Decimal128;

lib/types/objectid.js

@@ -8,7 +8,7 @@
  * @constructor ObjectId
  */
 
-var ObjectId = global.$MongooseDriver.ObjectId;
+var ObjectId = require('../driver').get().ObjectId;
 
 /*!
  * Getter for convenience with populate, see gh-6115