I had some trouble making something work in my Astro site.

I used Astro locals and I had to type a variable I shared using locals.

So I went and added that to the src/env.d.ts, as the docs say.

But my types weren’t picked up.

My code looked like this:

/// <reference types="astro/client" />
import { sometype } from 'somelib'

declare namespace App {
  interface Locals {
    somevariable: sometype
  }
}

What I discovered thanks to this SO answer is, we can’t do imports like this in .d.ts files.

So I imported the type in another file, and then I imported the type from that file, like this:

typesforenvdts.ts

import { sometype } from 'somelib'

export { sometype }

env.d.ts

/// <reference types="astro/client" />

declare namespace App {
  interface Locals {
    somevariable: import('./typesforenvdts').sometype
  }
}

Don’t ask me why, but now it works.

Lessons in this unit:

0:	Introduction
1:	Your first TypeScript program
2:	Types
3:	Typing functions
4:	The editor helps you with type errors
5:	Running TypeScript code
6:	Valid types
7:	Type aliases and interfaces
8:	Union types
9:	Typing arrays with generics
10:	The DX of editing TypeScript
11:	There's more...
12:	TypeScript declare a type that can be a string or array of strings
13:	TypeScript, disable checks for `declared but its value is never read`
14:	Object destructuring with types in TypeScript
15:	TypeScript Tutorial
16:	Zod: Type-Safe Schema Validation for TypeScript
17:	▶︎ How I fixed some trouble importing types in .d.ts files