Method changed

src/model.js:3895–3911

* If changed is called with a string it will return a boolean indicating whether the value of that key in `dataValues` is different from the value in `_previousDataValues`. * * If changed is called without an argument, it will return an array of keys that have changed. * * If changed is

(key, value)

   * @returns {boolean|Array}
   */
  changed(key, value) {
    if (key === undefined) {
      if (this._changed.size > 0) {
        return Array.from(this._changed);
      }
      return false;
    }
    if (value === true) {
      this._changed.add(key);
      return this;
    }
    if (value === false) {
      this._changed.delete(key);
      return this;
    }
    return this._changed.has(key);
  }

  /**
   * Returns the previous value for key from `_previousDataValues`.