SOURCE

class Book {
    constructor(title, pages, isbn){
        this.title = title
        this.pages = pages
        this.isbn = isbn
    };

    printIsbn(){
        console.log(this.isbn)
    }
}

let aBook = new Book("<阿凡达>", 50, 46513248)
aBook.title = "三毛流浪记"

class ITBook extends Book{
    constructor(title, pages, isbn, tech){
        super(title, pages, isbn)
        this.tech = tech
    }

    printTech(){
        console.log(this.tech)
    }
}

let itB = new ITBook("VUE", 50, 46513248, true)
console.log(itB.printTech())

<pre style="color: white;">
    1
    2
    2    3   e
    3
    3
</pre>