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ElementsKit

Qwik

A custom element built with elements-kit is just class extends HTMLElement registered via customElements.define. Qwik renders it fine at runtime, but Qwik’s JSX.IntrinsicElements is independent of elements-kit’s, so you need a small augmentation to get typed props, narrowed ref, and editor autocomplete on the Qwik side.

// shared element — built once, used anywhere
import { defineElement } from "elements-kit/custom-elements";
import { reactive } from "elements-kit/signals";


export class XCounter extends HTMLElement {
  @reactive() count = 0;
}


defineElement("x-counter", XCounter);

Source the prop shape from the class

Two helpers exported from elements-kit/jsx-runtime:

HelperShapeUse when
InstanceProps<I>Public instance fields only (drops the HTMLElement surface)You want to type just the user-defined props
ElementProps<C>Full elements-kit JSX surface — attrs, fields, events from static events, slots from [SLOTS], childrenYour element declares typed events or slots and you want callers to see them

For most Qwik wiring InstanceProps<XCounter> is enough.

Augment Qwik’s JSX.IntrinsicElements

import type { HTMLAttributes } from "@builder.io/qwik";
import type { InstanceProps } from "elements-kit/jsx-runtime";
import type { XCounter } from "./x-counter";


declare module "@builder.io/qwik" {
  namespace JSX {
    interface IntrinsicElements {
      "x-counter": HTMLAttributes<XCounter> & InstanceProps<XCounter>;
    }
  }
}


// <x-counter count={5} ref={counterRef} />  — typed

HTMLAttributes<XCounter> provides the standard HTML attribute surface (class, id, event handlers with $ suffix, …) and a ref signal narrowed to XCounter.

Co-locate the augmentation with the class

Put the declare module "@builder.io/qwik" block in the same file as the element class. Importing the class then brings the augmentation along — consumers don’t have to remember to write it themselves.

x-counter.ts
import { defineElement } from "elements-kit/custom-elements";
import { reactive } from "elements-kit/signals";
import type { HTMLAttributes } from "@builder.io/qwik";
import type { InstanceProps } from "elements-kit/jsx-runtime";


export class XCounter extends HTMLElement {
  @reactive() count = 0;
}


defineElement("x-counter", XCounter);


declare module "@builder.io/qwik" {
  namespace JSX {
    interface IntrinsicElements {
      "x-counter": HTMLAttributes<XCounter> & InstanceProps<XCounter>;
    }
  }
}

Typed document.querySelector and createElement

Independent of any framework, augmenting the global HTMLElementTagNameMap gives you typed lookups in plain DOM code:

declare global {
  interface HTMLElementTagNameMap {
    "x-counter": XCounter;
  }
}


const el = document.querySelector("x-counter"); // XCounter | null

Worth doing alongside the Qwik augmentation.

See also