Indexing into a select .options attribute doesn't return an HTMLOptionElement

[jasongrout]

TypeScript Version: 2.2.1

Code

let x = document.createElement('select');
x.appendChild(document.createElement('option'));

let z = x.options[0];
// Error, z is an Element, not an HTMLOptionElement
let value = z.value;

(http://www.typescriptlang.org/play/#src=let%20x%20%3D%20document.createElement('select')%3B%0D%0Ax.appendChild(document.createElement('option'))%3B%0D%0A%0D%0Alet%20z%20%3D%20x.options%5B0%5D%3B%0D%0A%2F%2F%20Error%2C%20z%20is%20an%20Element%2C%20not%20an%20HTMLOptionElement%0D%0Alet%20value%20%3D%20z.value%3B%0D%0A)

Expected behavior:

z should be typed as an HTMLOptionElement, allowing access to a .value property.

Actual behavior:

z is typed as an Element

I think this error was exposed when I moved my code from TS 2.1 to 2.2.

[jasongrout]

Possibly related to #9334 and #8220

[jasongrout]

It looks like it's getting the type from HTMLCollectionBase: https://github.com/Microsoft/TypeScript/blob/3e5b232e8816ff1af8b9ca2c04cee634ee86dc25/lib/lib.dom.d.ts#L4363

[RyanCavanaugh]

@mhegazy / @zhengbli seems like we should have this?

interface HTMLCollectionOf<T extends Element> extends HTMLCollection {
    [index: number]: T; // <-- add
    item(index: number): T;
    namedItem(name: string): T;
}

[jasongrout]

(For whoever may be reading this...) A work around for now is to use x.options.item(0), or of course you can cast the value.

[evmar]

@RyanCavanaugh looking at the blame for lib.dom.d.ts, it looks like it used to have that and an update to it lost it. When we updated Google to TS 2.2 we had to work around foo[i] with foo.item(i) in a bunch of places.

[jasongrout]

My example above now seems to work - I think this can be closed, at least for the select element. I'm not sure if other HTMLCollectionOf things work, since the change mentioned above has not been done.

[jasongrout]

@mhegazy / @zhengbli seems like we should have this?

This is done now: https://github.com/Microsoft/TypeScript/blob/2fbc2259a120c7be22397f01b6f99ce3c4306536/lib/lib.dom.d.ts#L13939