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<html><head> <title></title></head><body> <button>333</button> <script type="text/javascript"> var that ; class test { constructor(uname, age) { that = this; console.log(this) this.uname = uname this.age = age; this.btn = document.querySelector('button'); this.btn.onclick = this.sing; } sing() { //按钮点击的时候，this指向是调用者button，如果想要调用uname 需要用that这种方式 console.log(this) console.log(that.uname) } } class child extends test { constructor(uname, age) { // super(uname, age) //如果没有super（），直接调用sing， //sing里面的this是指向父类，没有定义会报错 this.uname = uname this.age = age; } } // var testObject = new test('lilie', 23) // testObject.sing() //this指向是test这个对象 var childObj = new child('lile', 25) childObj.sing() </script></body></html>