<!DOCTYPE html>
<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>