how to cancel subscription to window.cookieStore.addEventListener('change', ) in angular...

I have created an angular service which can listen to cookie changes by leveraging the CookieStore Api. My current code looks as follows:

type CookieChangeType = {
name: string,
value: string,
expires: Date,
domain: string,
}

interface CookieChangeEvent extends Event {
changed: CookieChangeType[]
}

type CookieStore = {
addEventListener: Window["addEventListener"]
}

declare global {
interface Window {
cookieStore: CookieStore;
addEventListener(type: String, listener: (this: Window, ev: CookieChangeEvent) => any, useCapture?: boolean): void;
}
}

export class CookieConsentCommonsService {


subscribeToConsentCookieChange(callback: () => void): void {
window.cookieStore.addEventListener('change', (event: CookieChangeEvent) => {
console.log(`Cookie changed: ${change.name} = ${change.value}`);
callback();
});
}
}


This code works as expected. On the top of that I would like to be able to cancel the subscription. I have tried to store the subscription for later :

const sub = window.cookieStore.addEventListener( ...);
console.log("sub " + sub)


But there is no return from this code and the output message is:

sub undefined


How can I retrieve a reference for created subscription and later on use it to cancel the subscription?

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