倒计时组件：如何防止Angular2中的重新渲染？

I have an Angular2 master component which includes a number of child components and an independant countdown component (named "clock" in the code below). Countdown component changes it's label every second and that causes the master component and all others to (needlessly) re-render. How can I prevent that? This is the source of my countdown component:I have an Angular2 master component which inclu