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<!DOCTYPE html> <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>