How can I use DOMStringMap in TypeScript?

Let's say I have a function:

angular.forEach(myElements, function prepareElements(myEl: HTMLElement, index) { myEl.dataset.myProperty = "whatever";
})

The problem I get is error TS2094: The property 'myProperty' does not exist on value of type 'DOMStringMap'

I don't really understand the interface in lib.d.ts

interface DOMStringMap {
}
declare var DOMStringMap: { prototype: DOMStringMap; new (): DOMStringMap;
}

then later on...

interface HTMLElement { dataset: DOMStringMap; hidden: boolean; msGetInputContext(): MSInputMethodContext;
}

Is it just me or is this a little unclear?

I tried casting it <DOMStringMap>myEl.dataset.myProperty = "whatever", which did nothing...

2 Answers

The DOMStringMap interface is empty because the spec is not finalized :

In the meantime you can simply use: myEl.dataset['myProperty'] = "whatever";

you can also cast it to user defined type

type IType = {myProperty: string}
....
(myEl.dataset) as IType.myProperty = "whatever";