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)

Start in lib.dom.d.ts and review the Element hierarchy and concrete SVG element declarations mentioned in the issue. Determine the intended scope for literal tagName types and how the declarations should support overloads and discriminated unions. Done means the relevant declarations provide the requested narrowing without changing runtime JavaScript behavior.