GlobalEventHandlers.onerror should be of type ErrorEventHandler | null

[thdk]

TypeScript Version: 3.2.1

Search Terms: lib.dom.ts GlobalEventHandlers onerror

Code

const imageEl = document.createElement("img");

// enable strictNullChecks in options and below line will give a type error
// type 'null' is not assignable to type 'ErrorEventHandler'
imageEl.onerror = null;

Expected behavior:
it should be possible to assign null to onerror

Actual behavior:
type 'null' is not assignable to type 'ErrorEventHandler'

Playground Link:
Playground link

Related Issues:
#28638 (not really related)

---

I believe line https://github.com/Microsoft/TypeScript/blob/master/lib/lib.dom.d.ts#L5478 can be modified to allow null as follows:
Option 1:

/**
     * Fires when an error occurs during object loading.
     * @param ev The event.
     */
    onerror: ErrorEventHandler | null;

Option 2

interface ErrorEventHandlerNonNull {
    (event: Event | string, source?: string, fileno?: number, columnNumber?: number, error?: Error): void;
}

and a type ErrorEventHandler

type ErrorEventHandler = ErrorEventHandlerNonNull | null;

and leave 'onerror: ErrorEventHandler;' as is.

[Fabianopb]

I've some spare time these weeks, I could take a look at this one too!

[Fabianopb]

I've checked the issue, apparently this is already implemented in the latest version (3.3.3333) using your Option2.

@thdk could you please check the following references and confirm that?

https://github.com/Microsoft/TypeScript/blob/v3.3.3333/lib/lib.dom.d.ts#L17115
https://github.com/Microsoft/TypeScript/blob/v3.3.3333/lib/lib.dom.d.ts#L17827

If that's true than @RyanCavanaugh can close the issue.

[thdk]

@Fabianopb seems to fixed indeed in 3.3.3333 👍

I'll close the issue.