<html><body><h1>JavaScript 类是以“严格模式”编写的</h1><p>在 JavaScript 类中，您不能在未声明的情况下使用变量。</p><p id="demo"></p><script>class Car { constructor(name, year) { this.name = name; this.year = year; } age() { // date = new Date(); // This will not work let date = new Date(); // This will work return date.getFullYear() - this.year; }}myCar = new Car("Ford", 2014);document.getElementById("demo").innerHTML ="My car is " + myCar.age() + " years old.";</script></body></html>