packages/add-months/.jsbits/proto.wrapper.js
function (_this, count, asUTC) {

    if (_this instanceof Date) {
      var date = $_NAME(_this, count, asUTC)
      return _this.setTime(+date)
    }

    throw new TypeError('Method Date.prototype.add' +
      (asUTC ? 'UTC' : '') + 'Months called on incompatible receiver ' + _this)
  }
function (_this, count, asUTC) {

    if (_this instanceof Date) {
      var date = $_NAME(_this, count, asUTC)
      return _this.setTime(+date)
    }

    throw new TypeError('Method Date.prototype.add' +
      (asUTC ? 'UTC' : '') + 'Months called on incompatible receiver ' + _this)
  }
#endif 
@param {Date} _this Date instance, may be null, NaN, etc
@param {number} count months to add
@param {boolean} asUTC utc date?