Typescript recognizing process.env variables as undefined despite being in environment.d.ts

Question

I had the impression that adding environment variables to environment.d.ts would ensure that they had the proper types.

I have @types/node as a dev-dependency, and have an environment.d.ts containing the following

declare global {
  namespace NodeJS {
    interface ProcessEnv {
      DATABASE_URL: string;
    }
  }
}

export {};

However, when I attempt to use DATABASE_URL, e.g. in

import PgPromise from "pg-promise";
const db = PgPromise()(process.env.DATABASE_URL || "");

I'm still getting the error

error TS2345: Argument of type 'string | undefined' is not assignable to parameter of type 'string | IConnectionParameters<IClient>'.
Type 'undefined' is not assignable to type 'string | IConnectionParameters<IClient>'.

Is there any way to ensure that DATABASE_URL is of type string, as opposed to string | undefined? Am I missing something?

Please edit your question to show where you're using that value. You can always use as string to convince TypeScript it's a string, see this answer to using process.env in TypeScript — Heretic Monkey
– Heretic Monkey, Commented Aug 28, 2021 at 19:25
To anyone that reads, sorry that I didn't include more details in my question. Was trying to limit it to what was relevant, but it seems I omitted the actual cause of the error as well. — blub
– blub, Commented Sep 9, 2021 at 18:52

blub · Accepted Answer · 2021-09-09 18:51:02Z

13

The error was coming from the fact that I was using ts-node.

I was using nodemon / ts-node, and ts-node uses files / include / exclude to determine what files to monitor. Because I didn't specify these, it wasn't able to detect my files.

I fixed it by adding

{
  ...,
  "ts-node": {
    "files": true
  },
  "include": ["src/**/*.ts", "environment.d.ts"]
}

to my tsconfig.json

answered Sep 9, 2021 at 18:51

blub

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1 Comment

Knightwalker Over a year ago

This was it! Also the default behaviour of include was "src/**/*" so if your environment.d.ts is inside src, then enabling only the ts-node/files flag also works. Did a little digging and on their website and they state that this flag helps with "certain typechecking failures" as in our case.

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