Components

Mutation Observer

<wa-mutation-observer> Since 2.0 Stable

The Mutation Observer component offers a thin, declarative interface to the MutationObserver API.

The mutation observer will report changes to the content it wraps through the wa-mutation event. When emitted, a collection of MutationRecord objects will be attached to event.detail that contains information about how it changed.

Click to mutate
👆 Click the button and watch the console 
<div class="mutation-overview">
  <wa-mutation-observer attr="variant">
    <wa-button variant="brand">Click to mutate</wa-button>
  </wa-mutation-observer>

  <br />
  👆 Click the button and watch the console

  <script>
    const container = document.querySelector('.mutation-overview');
    const mutationObserver = container.querySelector('wa-mutation-observer');
    const button = container.querySelector('wa-button');
    const variants = ['brand', 'success', 'neutral', 'warning', 'danger'];
    let clicks = 0;

    // Change the button's variant attribute
    button.addEventListener('click', () => {
      clicks++;
      button.setAttribute('variant', variants[clicks % variants.length]);
    });

    // Log mutations
    mutationObserver.addEventListener('wa-mutation', event => {
      console.log(event.detail);
    });
  </script>

  <style>
    .mutation-overview wa-button {
      margin-bottom: 1rem;
    }
  </style>
</div>

When you create a mutation observer, you must indicate what changes it should respond to by including at least one of attr, child-list, or char-data. If you don't specify at least one of these attributes, no mutation events will be emitted.

Examples

Child List

Use the child-list attribute to watch for new child elements that are added or removed.

Add button
👆 Add and remove buttons and watch the console 
<div class="mutation-child-list">
  <wa-mutation-observer child-list>
    <div class="buttons">
      <wa-button variant="brand">Add button</wa-button>
    </div>
  </wa-mutation-observer>

  👆 Add and remove buttons and watch the console

  <script>
    const container = document.querySelector('.mutation-child-list');
    const mutationObserver = container.querySelector('wa-mutation-observer');
    const buttons = container.querySelector('.buttons');
    const button = container.querySelector('wa-button[variant="brand"]');
    let i = 0;

    // Add a button
    button.addEventListener('click', () => {
      const button = document.createElement('wa-button');
      button.textContent = ++i;
      buttons.append(button);
    });

    // Remove a button
    buttons.addEventListener('click', event => {
      const target = event.target.closest('wa-button:not([variant="brand"])');
      event.stopPropagation();

      if (target) {
        target.remove();
      }
    });

    // Log mutations
    mutationObserver.addEventListener('wa-mutation', event => {
      console.log(event.detail);
    });
  </script>

  <style>
    .mutation-child-list .buttons {
      display: flex;
      gap: 0.25rem;
      flex-wrap: wrap;
      margin-bottom: 1rem;
    }
  </style>
</div>

Slots

Learn more about using slots.

Name Description
(default) The content to watch for mutations.

Attributes & Properties

Learn more about attributes and properties.

Name Description Reflects
attr
attr
Watches for changes to attributes. To watch only specific attributes, separate them by a space, e.g. attr="class id title". To watch all attributes, use *.
Type string
attrOldValue
attr-old-value
Indicates whether or not the attribute's previous value should be recorded when monitoring changes.
Type boolean
Default false
charData
char-data
Watches for changes to the character data contained within the node.
Type boolean
Default false
charDataOldValue
char-data-old-value
Indicates whether or not the previous value of the node's text should be recorded.
Type boolean
Default false
childList
child-list
Watches for the addition or removal of new child nodes.
Type boolean
Default false
disabled
disabled
Disables the observer.
Type boolean
Default false

Events

Learn more about events.

Name Description
wa-mutation Emitted when a mutation occurs.

Importing

The autoloader is the recommended way to import components. If you prefer to do it manually, use one of the following code snippets.

CDN npm React

To manually import this component from the CDN, use the following code. 

import 'https://early.webawesome.com/[email protected]/dist/components/mutation-observer/mutation-observer.js';
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