feat: new attachEffect utility

attach-effect/Counter.mjs

@@ -1,14 +1,22 @@
 // @ts-check
 import WebComponent from "../src/WebComponent.js";
-// import { attachEffect } from "../src/attach-effect.js";
+import { attachEffect } from "../src/attach-effect.js";
 
 export class Counter extends WebComponent {
   static properties = ["count"];
   onInit() {
     this.props.count = 0;
     this.onclick = () => ++this.props.count;
-    // attachEffect(this.props, 'count', console.log);
+    attachEffect(
+      this.props.count,
+      (count) => console.log(count)
+    );
   }
+
+  afterViewInit(){
+    attachEffect(this.props.count, (count) => console.log(count + 100));
+  }
+
   get template() {
     return `<button id="btn">${this.props.count}</button>`;
   }

src/WebComponent.js

@@ -24,7 +24,6 @@ export class WebComponent extends HTMLElement {
    * Read-only property containing camelCase counterparts of observed attributes.
    * @see https://www.npmjs.com/package/web-component-base#prop-access
    * @see https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/dataset
-   * @typedef {{[name: string]: any}} PropStringMap
    * @type {PropStringMap}
    */
   get props() {
@@ -53,11 +52,7 @@ export class WebComponent extends HTMLElement {
 
   /**
    * Triggered when an attribute value changes
-   * @param {{
-   *  property: string,
-   *  previousValue: any,
-   *  currentValue: any
-   * }} changes
+   * @param {Changes} changes
    */
   onChanges(changes) {}
 
@@ -125,7 +120,11 @@ export class WebComponent extends HTMLElement {
     }
   };
 
-  #handler(setter, typeMap) {
+  #effectsMap = {};
+
+  #handler(setter, meta) {
+    const effectsMap = meta.#effectsMap;
+    const typeMap = meta.#typeMap;
     const getKebab = (str) => {
       return str.replace(
         /[A-Z]+(?![a-z])|[A-Z]/g,
@@ -141,14 +140,25 @@ export class WebComponent extends HTMLElement {
           typeMap[prop] = typeof value;
         }
 
-        if (oldValue !== value) {
+        if (value.attach === "effect") {
+          if (!effectsMap[prop]) {
+            effectsMap[prop] = [];
+          }
+          effectsMap[prop].push(value.callback);
+        } else if (oldValue !== value) {
           obj[prop] = value;
+          effectsMap[prop]?.forEach((f) => f(value));
           const kebab = getKebab(prop);
           setter(kebab, value);
         }
 
         return true;
       },
+      get(obj, prop) {
+        Object.getPrototypeOf(obj[prop]).proxy = meta.#props;
+        Object.getPrototypeOf(obj[prop]).prop = prop;
+        return obj[prop];
+      },
     };
   }
 
@@ -156,13 +166,19 @@ export class WebComponent extends HTMLElement {
     if (!this.#props) {
       this.#props = new Proxy(
         {},
-        this.#handler(
-          (key, value) => this.setAttribute(key, value),
-          this.#typeMap
-        )
+        this.#handler((key, value) => this.setAttribute(key, value), this)
       );
     }
   }
 }
 
 export default WebComponent;
+
+/**
+ * @typedef {{
+ *  property: string,
+ *  previousValue: any,
+ *  currentValue: any
+ * }} Changes
+ * @typedef {{[name: string]: any}} PropStringMap
+ */

src/attach-effect.js

@@ -1,6 +1,15 @@
-export function attachEffect(proxy, prop, callback) {
-    proxy[prop] = {
-        attach: 'effect',
-        callback
-    }
+/**
+ *
+ * @typedef { import('./WebComponent.js').Changes} Changes
+ * @typedef { import('./WebComponent.js').PropStringMap} PropStringMap
+ * @param {Object} obj
+ * @param {(newValue: any) => void} callback
+ */
+export function attachEffect(obj, callback) {
+  const { proxy, prop } = Object.getPrototypeOf(obj);
+
+  proxy[prop] = {
+    attach: "effect",
+    callback,
+  };
 }