feat: attribure observer

application/source/dom/customelement.mjs

@@ -203,6 +203,7 @@ class CustomElement extends HTMLElement {
         this[internalSymbol] = new ProxyObserver({
             options: initOptionsFromAttributes(this, extend({}, this.defaults)),
         });
+        initAttributeChangeMutationObserver.call(this);        
         initOptionObserver.call(this);
         this[initMethodSymbol]();
     }
@@ -217,7 +218,9 @@ class CustomElement extends HTMLElement {
     }
 
     /**
-     * This method determines which attributes are to be monitored by `attributeChangedCallback()`.
+     * This method determines which attributes are to be
+     * monitored by `attributeChangedCallback()`. Unfortunately, this method is static.
+     * Therefore, the `observedAttributes` property cannot be changed during runtime.
      *
      * @return {string[]}
      * @since 1.15.0
@@ -421,7 +424,8 @@ class CustomElement extends HTMLElement {
 
         try {
             value = new Pathfinder(this[internalSymbol].getRealSubject()["options"]).getVia(path);
-        } catch (e) {}
+        } catch (e) {
+        }
 
         if (value === undefined) return defaultValue;
         return value;
@@ -491,7 +495,8 @@ class CustomElement extends HTMLElement {
             try {
                 initShadowRoot.call(self);
                 elements = self.shadowRoot.childNodes;
-            } catch (e) {}
+            } catch (e) {
+            }
 
             try {
                 initCSSStylesheet.call(this);
@@ -542,7 +547,8 @@ class CustomElement extends HTMLElement {
      * @return {void}
      * @since 1.7.0
      */
-    disconnectedCallback() {}
+    disconnectedCallback() {
+    }
 
     /**
      * The custom element has been moved into a new document (e.g. someone called document.adoptNode(el)).
@@ -550,7 +556,8 @@ class CustomElement extends HTMLElement {
      * @return {void}
      * @since 1.7.0
      */
-    adoptedCallback() {}
+    adoptedCallback() {
+    }
 
     /**
      * Called when an observed attribute has been added, removed, updated, or replaced. Also called for initial
@@ -595,6 +602,32 @@ class CustomElement extends HTMLElement {
     }
 }
 
+/**
+ * This method is called when the element is first created.
+ * 
+ * @private
+ * @this CustomElement
+ */
+function initAttributeChangeMutationObserver() {
+    const self = this;
+
+    if (self[attributeObserverSymbol] === undefined) {
+        self[attributeObserverSymbol] = {};
+    }
+
+    new MutationObserver(function (mutations) {
+        for (const mutation of mutations) {
+            if (mutation.type === "attributes") {
+                self.attributeChangedCallback(mutation.attributeName, mutation.oldValue, mutation.target.getAttribute(mutation.attributeName));
+            }
+        }
+    }).observe(self, {
+        attributes: true,
+        attributeOldValue: true,
+        attributeFilter: Object.keys(self[attributeObserverSymbol]),
+    });
+}
+
 /**
  * @this CustomElement
  * @private
@@ -787,7 +820,8 @@ function parseOptionsJSON(data) {
     try {
         let dataUrl = parseDataURL(data);
         data = dataUrl.content;
-    } catch (e) {}
+    } catch (e) {
+    }
 
     try {
         obj = JSON.parse(data);