Extract under the hood in TypeScript

Today we discuss Type Lookup

This is quite a rare case but if you need to match every element inside a union type by its field type (and you know in advance which one), that's what you need.

Let's take a look 👀

Filterting

This solution looks like what we did in Exclude under the hood:

We used Distributive Conditional Types which helped us filtering out the elements we need.

Here, we need to remove not matched (with type) elements of a union. Or in other words (if you don't like double negations as me 😅), we need to pick the union elements of a specific structure. We know in advance that the field is type. Let's try:

Also, if you're familiar with internal type Extract (it's the opposite what Exclude does), you can apply it here:

Great job 🔥

Please, don't hesitate to go to the test cases in Playground

Have a wonderful day 🌇