add js

examples/chapter02/js-class-example.js

@@ -0,0 +1,30 @@
+// 父类
+class Animal {
+    constructor(name) {
+        this.name = name;
+    }
+    speak() {
+        return "some animal sound";
+    }
+}
+
+// 子类
+class Dog extends Animal {
+    speak() {
+        return this.name +":  Woof!";
+    }
+}
+
+// 子类
+class Cat extends Animal {
+    speak() {
+        return this.name +":  Meow!";
+    }
+}
+
+// 使用
+let dog = new Dog("阿狗");
+let cat = new Cat("阿猫");
+
+console.log(dog.speak()); // 输出: Woof!
+console.log(cat.speak()); // 输出: Meow!