What is the best way to identify a particular subtype of HTMLElement based on its tag name and then save that element within another one?

I have a function that generates a node and returns it. Here is an example implementation:

addElement: function ({
    parentNode,
    elementName,
    tagName,
  }) {
    // Creates and appends the new node.
    parentNode[elementName] = document.createElement(tagName);
    parentNode.appendChild(parentNode[elementName]);

    return parentNode[elementName];
  }

In this function, parentNode refers to another element, elementName is a string (e.g., container), and tagName specifies the type of element being created, also in string form (e.g., div).

The issue I am facing is uncertainty regarding the exact type that will be returned. The return type could be an extension of Element, which might be HTMLDivElement or HTMLAreaElement. Similarly, determining the type of parentNode presents a challenge as well.

How can I resolve this in TypeScript?

javascripttypescriptdom

Answer №1

One of the key questions being raised here is:

How do I create a specific subtype of HTMLElement based on its tag name?

The function provided in the example uses document.createElement(tagName) to generate an element that is then returned.

An examination of the TypeScript DOM library source reveals that the signature for document.createElement is as follows:

  • The first overload signature returns a specific subtype of HTMLElement when the tagName matches a key in the HTMLElementTagNameMap interface.

  • The second signature deals with deprecated elements, which is not considered in this response.

  • The final signature returns a generic HTMLElement if the tag name is not recognized.

By utilizing generic constraints, it is possible to create a type utility that derives a specific element type from the tag name map or defaults to HTMLElement in case the tag name is unrecognized:

...

To address associating arbitrary data with a DOM node, JavaScript provides the WeakMap feature. This can be used to store additional information related to DOM nodes. By using a WeakMap, you can avoid directly manipulating objects you don't own.

...

In conclusion, the final code has been consolidated into a single playground for reference:

TS Playground

type HtmlElementFromTagName<TagName extends string> =
  TagName extends keyof HTMLElementTagNameMap
  ? HTMLElementTagNameMap[TagName]
...
const addElementToNode = (
  node: Node,
  ...
};
const getElementFromNode = (
  node: Node,
  ...
};

type AddElementProps<TagName extends string>
...
const addElement = <TagName extends string>(
  { elementName, parentNode, tagName }: AddElementProps<TagName>
) => {
  const element = document.createElement(tagName) as HtmlElementFromTagName<TagName>;
  ...
};

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