fix mutation observer in react

docs/components/mutation-observer.md

@@ -8,7 +8,7 @@ The mutation observer will report changes to the content it wraps through the `s
 
 ```html preview
 <div class="mutation-overview">
-  <sl-mutation-observer attr>
+  <sl-mutation-observer attr="type">
     <sl-button type="primary">Click to mutate</sl-button>
   </sl-mutation-observer>
 
@@ -42,6 +42,47 @@ The mutation observer will report changes to the content it wraps through the `s
 </div>
 ```
 
+```jsx react
+import { useState } from 'react';
+import { SlButton, SlMutationObserver } from '@shoelace-style/shoelace/dist/react';
+
+const css = `
+  .resize-observer-overview div {
+    display: flex; 
+    border: solid 2px rgb(var(--sl-input-border-color)); 
+    align-items: center; 
+    justify-content: center;
+    text-align: center;
+    padding: 4rem 2rem;
+  }
+`;
+
+const types = ['primary', 'success', 'neutral', 'warning', 'danger']; 
+let clicks = 0;
+
+const App = () => {
+  const [type, setType] = useState('primary');
+
+  function handleClick() {
+    clicks++;
+    setType(types[clicks % types.length]);
+  }
+
+  return (
+    <>
+      <SlMutationObserver 
+        attr="*"
+        onSlMutation={event => console.log(event.detail)}
+      >
+        <SlButton type={type} onClick={handleClick}>Click to mutate</SlButton>
+      </SlMutationObserver>
+
+      <style>{css}</style>
+    </>
+  );
+};
+```
+
 ?> 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
@@ -101,4 +142,55 @@ Use the `child-list` attribute to watch for new child elements that are added or
 </div>
 ```
 
+```jsx react
+import { useState } from 'react';
+import { SlButton, SlMutationObserver } from '@shoelace-style/shoelace/dist/react';
+
+const css = `
+  .mutation-child-list .buttons {
+    display: flex;
+    gap: .25rem;
+    flex-wrap: wrap;
+    margin-bottom: 1rem;
+  }
+`;
+
+let buttonCount = 0;
+
+const App = () => {
+  const [buttonIds, setButtonIds] = useState([]);
+
+  function addButton() {
+    setButtonIds([...buttonIds, ++buttonCount]);
+  }
+
+  function removeButton(id) {
+    setButtonIds(buttonIds.filter(i => i !== id));
+  }
+
+  return (
+    <>
+      <div class="mutation-child-list">
+        <SlMutationObserver 
+          child-list 
+          onSlMutation={event => console.log(event.detail)}
+        >
+          <div class="buttons">
+            <SlButton type="primary" onClick={addButton}>Add button</SlButton>
+            {buttonIds.map(id => (
+              <SlButton key={id} type="default" onClick={() => removeButton(id)}>
+                {id}
+              </SlButton>
+            ))}
+          </div>
+        </SlMutationObserver>
+      </div>
+
+      👆 Add and remove buttons and watch the console
+      <style>{css}</style>
+    </>
+  );
+};
+```
+
 [component-metadata:sl-mutation-observer]

docs/resources/changelog.md

@@ -9,6 +9,7 @@ _During the beta period, these restrictions may be relaxed in the event of a mis
 ## Next
 
 - Added React examples and CodePen links to all components
+- Changed the `attr` in experimental `<sl-mutation-observer>` to require `"*"` instead of `""` to target all attributes
 - Fixed a bug in `<sl-progress-bar>` where the `label` attribute didn't set the label
 - Fixed a bug in `<sl-rating>` that caused disabled and readonly controls to transition on hover
 - The `panel` property of `<sl-tab>` is now reflected

src/components/mutation-observer/mutation-observer.ts

@@ -19,8 +19,8 @@ export default class SlMutationObserver extends LitElement {
   private mutationObserver: MutationObserver;
 
   /**
-   * Watches for changes to attributes. If empty, all changes will be reported. To watch only specific attributes,
-   * separate them by a space.
+   * Watches for changes to attributes. If set to *, all changes will be reported. To watch only specific attributes,
+   * separate them by a space, e.g. "class id title".
    */
   @property({ reflect: true }) attr: string;
 
@@ -80,12 +80,15 @@ export default class SlMutationObserver extends LitElement {
   }
 
   startObserver() {
+    const observeAttributes = typeof this.attr === 'string' && this.attr.length > 0;
+    const attributeFilter = observeAttributes && this.attr !== '*' ? this.attr.split(' ') : undefined;
+
     try {
       this.mutationObserver.observe(this, {
         subtree: true,
         childList: this.childList,
-        attributes: typeof this.attr === 'string',
-        attributeFilter: typeof this.attr === 'string' && this.attr.length > 0 ? this.attr.split(' ') : undefined,
+        attributes: observeAttributes,
+        attributeFilter,
         attributeOldValue: this.attrOldValue,
         characterData: this.charData,
         characterDataOldValue: this.charDataOldValue