CODEWITHSUNDEEP
javascripthtmldomweb-componentshadow-dom
kofifus
kofifus

Reputation: 19295

shadow dom - know when dom is rendered/changed

I am writing a chrome extension that modifies elements properties as a page is loaded or changes.

I do this using a Mutation Observer. However the observer's handler is not called when shadow-dom (ie, embedded twitter posts) are loaded/changed.

Is there a way to get an event when shadow-dom is loaded/changes or to hook a mutation observer to it ?

Thanks!

Upvotes: 6

Views: 6138

Answers (2)

jimmont
jimmont

Reputation: 2544

if the contents are simply getting slotted using the slotchange event is easiest, it doesn't fire on deeper changes, just the slotting (unlike a mutation observer watching a subtree and childList); it's like an observer of childList on the slot and the best way to separate concerns between a component and slotted content; when observing changes in a component's own respective shadowRoot or deeper in a tree for some reason, use the mutation observer in @Supersharp's answer except adding subtree to the config (or possibly setup children with their respective shadowRoots to dispatch an event with {composed: true, cancelable: true, bubbles: true} notifying ancestors up to your component of the change;

there'd need to be a slot added to the shadowRoot and the event listener added to it like shadowRoot.innerHTML = <slot onslotchange=...>empty slot</slot> adapted to work in-context

https://developer.mozilla.org/docs/Web/API/HTMLSlotElement/slotchange_event

Upvotes: 0

Supersharp
Supersharp

Reputation: 31181

You can simply observe() the shadowRoot property of the element with a Shadow DOM.

customElements.define('image-list', class extends HTMLElement {
  connectedCallback() {
    var observer = new MutationObserver(function(mutations) {
      mutations.forEach(function(mutation) {
        //Detect <img> insertion
        if (mutation.addedNodes.length)
          console.info('Node added: ', mutation.addedNodes[0])
      })
    })

    this.attachShadow({mode: 'open'}).innerHTML = '<img alt="image 1">'

    observer.observe(this.shadowRoot, {childList: true})
  }

  addImage() {
    var img = document.createElement('img')
    img.alt = ' new image '
    this.shadowRoot.appendChild(img)
  }
})
<image-list id=LI>
</image-list>
<button onclick="LI.addImage()">Add image</button>

Upvotes: 12

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