Observe shadow root on connected callback

docs/_guide/rendering-2.md

@@ -89,7 +89,7 @@ class HelloWorldElement extends HTMLElement {
   }
 
   attributeChangedCallback() {
-    render(() => html`
+    render(html`
       <div>
         Hello <span>${ this.name }</span>
       </div>`,
@@ -125,7 +125,7 @@ class HelloWorldElement extends HTMLElement {
   }
 
   update() {
-    render(() => html`
+    render(html`
       <div>
         Hello <span>${ this.#name }</span>
       </div>`,

docs/_guide/rendering.md

@@ -66,7 +66,7 @@ class HelloWorldElement extends HTMLElement {
   }
 
   attributeChangedCallback() {
-    render(() => html`
+    render(html`
       <div>
         Hello <span>${ this.name }</span>
       </div>`,
@@ -102,7 +102,7 @@ class HelloWorldElement extends HTMLElement {
   }
 
   update() {
-    render(() => html`
+    render(html`
       <div>
         Hello <span>${ this.#name }</span>
       </div>`,

src/core.ts

@@ -3,6 +3,7 @@ import {bind, bindShadow} from './bind.js'
 import {autoShadowRoot} from './auto-shadow-root.js'
 import {defineObservedAttributes, initializeAttrs} from './attr.js'
 import type {CustomElementClass} from './custom-element.js'
+import {observe} from './lazy-define.js'
 
 const symbol = Symbol.for('catalyst')
 
@@ -57,7 +58,10 @@ export class CatalystDelegate {
     initializeAttrs(instance)
     bind(instance)
     connectedCallback?.call(instance)
-    if (instance.shadowRoot) bindShadow(instance.shadowRoot)
+    if (instance.shadowRoot) {
+      bindShadow(instance.shadowRoot)
+      observe(instance.shadowRoot)
+    }
   }
 
   disconnectedCallback(element: HTMLElement, disconnectedCallback: () => void) {

src/lazy-define.ts

@@ -55,21 +55,24 @@ const strategies: Record<string, Strategy> = {
   visible
 }
 
-const timers = new WeakMap<Element, number>()
-function scan(node: Element) {
-  cancelAnimationFrame(timers.get(node) || 0)
+type ElementLike = Element | Document | ShadowRoot
+
+const timers = new WeakMap<ElementLike, number>()
+function scan(element: ElementLike) {
+  cancelAnimationFrame(timers.get(element) || 0)
   timers.set(
-    node,
+    element,
     requestAnimationFrame(() => {
       for (const tagName of dynamicElements.keys()) {
-        const child: Element | null = node.matches(tagName) ? node : node.querySelector(tagName)
+        const child: Element | null =
+          element instanceof Element && element.matches(tagName) ? element : element.querySelector(tagName)
         if (customElements.get(tagName) || child) {
           const strategyName = (child?.getAttribute('data-load-on') || 'ready') as keyof typeof strategies
           const strategy = strategyName in strategies ? strategies[strategyName] : strategies.ready
           // eslint-disable-next-line github/no-then
           for (const cb of dynamicElements.get(tagName) || []) strategy(tagName).then(cb)
           dynamicElements.delete(tagName)
-          timers.delete(node)
+          timers.delete(element)
         }
       }
     })
@@ -82,17 +85,20 @@ export function lazyDefine(tagName: string, callback: () => void) {
   if (!dynamicElements.has(tagName)) dynamicElements.set(tagName, new Set<() => void>())
   dynamicElements.get(tagName)!.add(callback)
 
-  scan(document.body)
+  observe(document)
+}
 
-  if (!elementLoader) {
-    elementLoader = new MutationObserver(mutations => {
-      if (!dynamicElements.size) return
-      for (const mutation of mutations) {
-        for (const node of mutation.addedNodes) {
-          if (node instanceof Element) scan(node)
-        }
+export function observe(target: ElementLike): void {
+  elementLoader ||= new MutationObserver(mutations => {
+    if (!dynamicElements.size) return
+    for (const mutation of mutations) {
+      for (const node of mutation.addedNodes) {
+        if (node instanceof Element) scan(node)
       }
-    })
-    elementLoader.observe(document, {subtree: true, childList: true})
-  }
+    }
+  })
+
+  scan(target)
+
+  elementLoader.observe(target, {subtree: true, childList: true})
 }

test/controller.ts

@@ -1,7 +1,8 @@
 import {expect, fixture, html} from '@open-wc/testing'
-import {replace, fake} from 'sinon'
+import {replace, fake, spy} from 'sinon'
 import {controller} from '../src/controller.js'
 import {attr} from '../src/attr.js'
+import {lazyDefine} from '../src/lazy-define.js'
 
 describe('controller', () => {
   let instance
@@ -65,6 +66,23 @@ describe('controller', () => {
     expect(instance.foo).to.have.callCount(1)
   })
 
+  it('observes changes on shadowRoots', async () => {
+    const onDefine = spy()
+    lazyDefine('nested-shadow-element', onDefine)
+
+    @controller
+    class ControllerObserveShadowElement extends HTMLElement {
+      connectedCallback() {
+        const shadowRoot = this.attachShadow({mode: 'open'})
+        // eslint-disable-next-line github/unescaped-html-literal
+        shadowRoot.innerHTML = '<div><nested-shadow-element></nested-shadow-element></div>'
+      }
+    }
+    instance = await fixture<ControllerObserveShadowElement>(html`<controller-observe-shadow />`)
+
+    expect(onDefine).to.be.callCount(1)
+  })
+
   it('binds auto shadowRoots', async () => {
     @controller
     class ControllerBindAutoShadowElement extends HTMLElement {

test/lazy-define.ts

@@ -1,6 +1,6 @@
 import {expect, fixture, html} from '@open-wc/testing'
 import {spy} from 'sinon'
-import {lazyDefine} from '../src/lazy-define.js'
+import {lazyDefine, observe} from '../src/lazy-define.js'
 
 const animationFrame = () => new Promise<unknown>(resolve => requestAnimationFrame(resolve))
 
@@ -45,6 +45,21 @@ describe('lazyDefine', () => {
 
       expect(onDefine).to.be.callCount(2)
     })
+
+    it('lazy loads elements in shadow roots', async () => {
+      const onDefine = spy()
+      lazyDefine('nested-shadow-element', onDefine)
+
+      const el = await fixture(html` <div></div> `)
+      const shadowRoot = el.attachShadow({mode: 'open'})
+      observe(shadowRoot)
+      // eslint-disable-next-line github/unescaped-html-literal
+      shadowRoot.innerHTML = '<div><nested-shadow-element></nested-shadow-element></div>'
+
+      await animationFrame()
+
+      expect(onDefine).to.be.callCount(1)
+    })
   })
 
   describe('firstInteraction strategy', () => {