text: 'use strict';
  
  module.exports = function diffKeys(object) {
    let objectToDiff;
  
    if (object instanceof this.constructor) {
      objectToDiff = object.all();
    } else {
      objectToDiff = object;
    }
  
    const objectKeys = Object.keys(objectToDiff);
  
    const remainingKeys = Object.keys(this.items)
      .filter(item => objectKeys.indexOf(item) === -1);
  
    return new this.constructor(this.items).only(
      remainingKeys,
    );
  };
  