Typescript declaration merging / type augmentations

tsconfig.json

{
  "//1//":"This doesn't seem to be needed",
  "compilerOptions": {
    // ... your setup
    "typeRoots": ["./custom.d.ts"] // Aka add these types on top of the other ones
  }
}

types.ts

import * as admin from "firebase-admin"


declare global
{
	// eslint-disable-next-line @typescript-eslint/no-namespace
	namespace Express
	{
		export interface Request
		{
			user: admin.auth.DecodedIdToken
		}

		interface Session
		{
		}
	}
}


interface Array<T>
{
	last(): T | undefined
}