Chrome, Safari, and Opera (because of Blink) have implemented Custom Elements and Shadow DOM. Firefox appears to be working on it, and for Edge it's high priority, so things are coming along nicely :)
edit: The polyfills are also very viable. I know sometimes people knock polyfills, but they're really just libraries that implement the component model and encapsulation that frameworks generally have to, but they go away over time.
edit: The polyfills are also very viable. I know sometimes people knock polyfills, but they're really just libraries that implement the component model and encapsulation that frameworks generally have to, but they go away over time.