Error TS2339: Property 'customProperty' does not exist on type 'Window & typeof globalThis'

I encountered Error TS2339: Property 'customFunction' does not exist on type 'Window & typeof globalThis'. when trying to build my Angular library.

I am trying to add .d.ts file in my freshly generated library and still encountered the issue during build. I tried the solution from multiple questions here, and yet I still encountered the issue.

Here my steps to replicate:

First I generated new workspace:

ng new test-workspace --create-application=false

Then, inside the workspace, I generate a new Angular Library

cd test-workspace

ng generate library lib-test

After that, I generated a directory in lib-test under lib-test/src/types.

Then, I created a file window.d.ts with following content

declare global { 
    interface Window {
        customFunction: {
            startService: (arg: string) => void;
            endService: (arg: string) => void;
        }
    }
}

export {};

After that, I called window with the custom property in the lib-test.service.ts

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root'
})
export class LibTestService {

  constructor() { 
    window.customFunction.startService("test");
  }
}

On VSCode, there aren't any error Property 'customFunction' does not exist on type 'Window & typeof globalThis'.. But during ng build lib-test, I encountered this error. Can someone help to point out am I missing any steps for implementing this customFunction?

Alternative:

Try adding types to the tsconfig.

{
  "extends": "../../tsconfig.json",
  "compilerOptions": {
    "outDir": "../../out-tsc/lib",
    "declaration": true,
    "declarationMap": true,
    "inlineSources": true,
    "types": ["./src/types/index.d.ts"]
  },
  "exclude": ["**/*.spec.ts"]
}

Stackblitz Demo -> npm i -> cd test-workspace -> npm i -> cd projects/lib-test -> npm i -> ng build lib-test

Original Fix:

The fix for the issue is to add the reference to the type using the triple slash include syntax.

/*
* Public API Surface of lib-test
*/
/// <reference path="./types/index.d.ts" />
export * from './lib/lib-test.service';
export * from './lib/lib-test.component';

After doing this the build was successful, The below github issue helped me find the solution (Comment from dherges.

How to add custom typings to a library build? #193

Stackblitz Demo -> npm i -> cd test-workspace -> npm i -> cd projects/lib-test -> npm i -> ng build lib-test