Type the tagName string property of Element derivations to aid overloading and for discriminated unions

Search Terms

tagName, nodeName

Suggestion

Typing the tagName property in lib.dom.d.ts for Element and derivations ( or only concrete derivations and a discriminated type alias of these )
e.g
interface SVGGElement extends SVGGraphicsElement {
//..existing definition
tagName:"g"
}

Use Cases

Simpler to write overloads, overloaded by single argument type ( order does not matter )
Discriminated Unions

Examples

interface SVGCircleElement{
tagName:"circle"
}
interface SVGGElement{
tagName:"g"
}
interface SVGRectElement{
tagName:"rect"
}

Without above order matters with overload
adopt(node: SVGGElement): G;//issue with this before circle overload
adopt(node: SVGCircleElement): Circle;

With above and
type SVGTestUnionType=SVGCircleElement|SVGRectElement;

function(circleOrG:SVGTestUnionType){
switch(circleOrG.tagName){
case "circle":
//circle members available
break;
case "rect":
//rect members available
break;
}
}

Checklist

My suggestion meets these guidelines: YES

• This wouldn't be a breaking change in existing TypeScript / JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. new expression-level syntax)

Inizia in lib.dom.d.ts ed esamina la gerarchia di Element e le dichiarazioni degli elementi SVG concreti menzionate nell’issue. Determina l’ambito previsto per i tipi letterali di tagName e come le dichiarazioni debbano supportare gli overload e le unioni discriminate. Il lavoro è completo quando le dichiarazioni pertinenti forniscono il narrowing richiesto senza modificare il comportamento di JavaScript a runtime.