Filtering union of strings with suffix

Question

I have this line of code:

type RouterQuery = keyof AppRouter['_def']['queries'];

Which will give me this type:

type RouterQuery = "healthz" | "post.all" | "post.byId" | "category.all" | "category.byId" | "course.all" | "course.featured"

I'm trying to get only strings that have an '.all' postfix.

The desired type would be:

type RouterQueryAll = "post.all" | "category.all" | "course.all"

How can I do that?

Answer 1

type RouterQueryAll = Extract<RouterQuery, `${string}.all`>

Using Extract, you can ‘filter’/extract types from a union that are assignable to another type. `${string}.all` is an example of a template literal type that matches all strings ending in .all.