addEventListener for message on Window or Worker

[mjgreen145]

Search Terms: Window, Worker, addEventListener, union types

Code
I have a function which can either accept a Window or a Worker - there are many similarities between the two - and I want to be able to use common methods without caring about which of the two types the argument is. This function works if the argument w is set to be either Window or Worker in isolation, but not if it's the union type.

function myFunc(w: Worker | Window): void {
    const handler = (message: MessageEvent): any => {console.log(message)};
    w.addEventListener<"message">('message', handler);
}

Both Window.addEventListener and Worker.addEventListener have an overloaded type definition of:

addEventListener<K extends keyof WorkerEventMap>(type: K, listener: (this: Worker, ev: WorkerEventMap[K]) => any, options?: boolean | AddEventListenerOptions): void;

Expected behavior:
No problems

Actual behavior:
<"message"> part throws an error - Typescript seems to only want to use the non-generic version of the addEventListener function, which my example doesn't fit since MessageEvent cannot be cast to Event.

Playground Link:
http://www.typescriptlang.org/play/#code/MYewdgzgLgBA7gRgFwwOoEswBMRxgXnkxzgG4AoUSWOAJhVRACcBrAUyYJjDb0dY4AKAOTCAlKRjlyAMwCuYYFHTgYAWwCeAMQXBBcBs3acAPmmK4xKAG4h0WGAG9yMVzCrQYACwCG2ADYcXIJqbBAQPgDmbCgAsmER0QCi1mxgUFYwfhoEAHxOHiCBAHT+IJEhCVFsYgC+FG7wxT5YWClpUAAy6NBpHAA8AESh4dWDuSIjiWzCADTefliBTBLktUA

[nmain100]

Duplicate of #7294.

In fact, Window does not have the signature you're looking for, it has

addEventListener<K extends keyof WindowEventMap>(...)

This signature behaves equivalently to the worker scope one when K = "message", but that's not enough to merge the call signatures.

[mjgreen145]

Ok, thanks. Will close this and follow linked thread.