Demystifying Taiga UI root component: portals pattern in Angular

Just before new year, Roman, my colleague, announced our new Angular UI kit library Taiga UI. If you go through Getting started steps, you will see that you need to wrap your app with the tui-root component. Let's see what it does and explore what portals are and how and why we use them.

What is a portal?

Imagine you have a select component. It has a drop-down block with suggestions. If we keep it at the same position in DOM as the hosting component, we will run into all sorts of trouble. Items pop through and containers can chop off content:

Verticality issues are often solved with z-index, effectively starting World War Z in your app. It's not uncommon to see values like 100, 10000, 10001. But even if you manage to get it right — overflow: hidden would still get you there. So what can we do? Instead of having drop-down near its host we can show it in a dedicated container on top of everything. Then your application content can live in its own isolated context eliminating z-index problems. This container is exactly what a portal is. And it is what the Taiga UI root component sets up for you, among other…