构造函数等同成员变量

class Student {
    fullName: string;
    constructor(public firstName, public middleInitial, public lastName) {
        this.fullName = firstName + " " + middleInitial + " " + lastName;
    }
}

interface Person {
    firstName: string;
    lastName: string;
}

function greeter(person : Person) {
    return "Hello, " + person.firstName + " " + person.lastName;
}

let user = new Student("Jane", "M.", "User");

document.body.innerHTML = greeter(user);

还要注意的是，在构造函数的参数上使用public等同于创建了同名的成员变量。 意思是说

class Student {
    fullName: string;
    constructor(public firstName, public middleInitial, public lastName) {
        this.fullName = firstName + " " + middleInitial + " " + lastName;
    }
}

等同于

class Student {
    fullName: string;
    firstName:string;
    middleInitial:string;
    lastName:string;
    constructor( firstName,  middleInitial,  lastName) {
        this.fullName = firstName + " " + middleInitial + " " + lastName;
    }
}