Request to change currentTarget in Event interface for lib.d.ts

[nathggns]

When using the Event interface from lib.d.ts, and attaching a listener, the callback will get an object of type Event. However, the Event's currentTarget property is of type EventTarget (whereas it's should be of type Element/HTMLElement).

[saschanaz]

XMLHttpRequest object also can be currentTarget but it is not Element/HTMLElement. Maybe that's the reason behind this. Would generic type improve this?

interface Event<T extends EventTarget> {
    /* ... */
    currentTarget: T;
    /* ... */
}

interface EventListener<T extends EventTarget> {
    (evt: Event<T>): void;
}

interface HTMLElement {
    /* ... */
    addEventListener(type: string, listener: EventListener<HTMLElement>, useCapture?: boolean): void;
}

[nathggns]

Looks like it'll go a long way to improving it.

Sent from my iPhone

On 3 Aug 2014, at 13:34, SaschaNaz notifications@github.com wrote:

XMLHttpRequest object also can be currentTarget but it is not Element/HTMLElement. Maybe that's the reason behind this. Would generic type improve this?

interface Event {
/* ... /
currentTarget: T;
/ ... */
}

interface EventListener {
(evt: Event): void;
}

interface HTMLElement {
/* ... */
addEventListener(type: string, listener: EventListener, useCapture?: boolean): void;
}
—
Reply to this email directly or view it on GitHub.

[RyanCavanaugh]

Note that not every event target is an Element (http://www.w3.org/TR/DOM-Level-3-Events/#event-types), so the solution here would have to be more along the lines of @saschanaz's suggestion.

The problem is that we currently generate lib.d.ts, using a script, based on a file which we can't make public at this time, and that file is being deprecated in favor of a new one. Because of that, we're not going to make improvements in the script at this time, but hopefully in the future we can take PRs on the lib.d.ts generation script/input.

Tagging 'Revisit' for now - please ping us on this in a month and I can see where we're at.

[saschanaz]

Is there any syntax to refer the current type? I think this can be solved more easily if we can do this kind of work:

interface HTMLElement {
    addEventListener(type: string, listener: EventListener<this>, useCapture?: boolean): void;
}

var image: HTMLImageElement;
var video: HTMLVideoElement;
image.addEventListener // receives EventListener<HTMLImageElement> type
video.addEventListener // receives EventListener<HTMLVideoElement> type

[danquirk]

That functionality does not exist, it's something akin to what's suggested in #285 and #229

[rayshan]

Hi all, pinging this thread. I ran into this issue with Event.target. I would imagine most of the time a target is an HTMLElement. It is a little odd that the default type assumes it isn't. I tried @saschanaz's suggestion and ran into the "duplicate identifier" issue (sorry I may be missing something, I'm pretty new to TypeScript).

Edit: this worked to quiet the warnings: (<HTMLElement>event.target).tagName

[kitsonk]

@rayshan the suggestion was for what should go into the lib.d.ts file and the file is auto generated based directly on the implementation of Internet Explorer. So the error you encountered is accurate. Right now the only way around it is to build without the built in lib (--noLib) and use the workaround, or do what you have done, which is cast the target. There are currently a number of challenges of dealing with the return types of the DOM right now in TypeScript (mostly because the DOM isn't the most consistent/structured/type safe/consistently implemented set of APIs).