"use strict"; var _obj; const Base = {}; const obj = _obj = { set() { return babelHelpers.set(babelHelpers.getPrototypeOf(_obj), "test", 3, this, true); } }; Object.setPrototypeOf(obj, Base); expect(obj.set()).toBe(3); expect(Base.test).toBeUndefined(); expect(obj.test).toBe(3);