JavaScript 继承 - 值未定义

Question

有人可以解释一下为什么如果我调用greet函数，firstName和lastName是未定义的吗？ 似乎两者都设置正确，所以我真的不知道出了什么问题。我应该做什么来解决它。

'use strict';

class Person {
    constructor() {
        this.firstName = 'James';
        this.lastName = 'Bond';
    }

    greet() {
        console.log(`Hello ${this.firstname} ${this.lastname}`);
    }
}

class Employee extends Person {
    constructor() {
        super();
        this.salary = 1234;
    }
}

var employee = new Employee();

console.log(employee.firstName); //James
console.log(employee.lastName); //Bond
console.log(employee.salary); //1324

employee.greet(); //Hello undefined undefined

Answer 1

JavaScript 非常区分大小写... firstname != firstName

你想要:

console.log(`Hello ${this.firstName} ${this.lastName}`);
                               ^                ^