How to tell typescript, that process is not undefined?

Question

In the following line of code:

internalWhiteList = process.env.INTERNAL_IP_WHITELIST.split( ',' )

I get an error saying, Object is possibly undefined. env variables are loaded into process.env using the module named dotenv from .env file placed at the root.

How could I tell typescript, that process is not undefined? Here is my tsconfig.json:

    {
    "compilerOptions": {
        "target": "esnext",
        "outDir": "../dist",
        "allowJs": true,
        "module": "commonjs",
        "noEmitOnError": false,
        "noImplicitAny": false,
        "strictNullChecks": true,
        "sourceMap": true,
        "pretty": false,
        "removeComments": true,
        "listFiles": false,
        "listEmittedFiles": false
    },
    "exclude": [
        "node_modules",
        "test/",
        "**/*.spec.ts"
    ]
}

Answer 1

Maybe with a non-null assertion operator (!):

internalWhiteList = process.env.INTERNAL_IP_WHITELIST!.split( ',' )

Or with a if statement:

if (process.env.INTERNAL_IP_WHITELIST)
  internalWhiteList = process.env.INTERNAL_IP_WHITELIST.split( ',' )

What does it mean???

If you look at the type-defs for Node you see:

export interface ProcessEnv {
    [key: string]: string | undefined;
}

It's that string | undefined that means INTERNAL_IP_WHITELIST is possibly undefined, in which case undefined.split() is an error, so you need to assert or guard against it being undefined (as this answer demonstrates).