fix(document): support calling Document constructor directly in Node.js

Fix #8237

Author: vkarpov15

lib/document.js

@@ -10,6 +10,7 @@ const MongooseError = require('./error/index');
 const MixedSchema = require('./schema/mixed');
 const ObjectExpectedError = require('./error/objectExpected');
 const ObjectParameterError = require('./error/objectParameter');
+const Schema = require('./schema');
 const StrictModeError = require('./error/strict');
 const ValidatorError = require('./schematype').ValidatorError;
 const VirtualType = require('./virtualtype');
@@ -64,6 +65,17 @@ function Document(obj, fields, skipId, options) {
   }
   options = options || {};
 
+  // Support `browserDocument.js` syntax
+  if (this.schema == null) {
+    const _schema = utils.isObject(fields) && !fields.instanceOfSchema ?
+      new Schema(fields) :
+      fields;
+    this.$__setSchema(_schema);
+    fields = skipId;
+    skipId = options;
+    options = arguments[4] || {};
+  }
+
   this.$__ = new InternalCache;
   this.$__.emitter = new EventEmitter();
   this.isNew = 'isNew' in options ? options.isNew : true;