无法从javascript中的子类访问父类变量
无法从javascript中的子类访问父类变量
提问于 2018-09-27 04:21:09
我有两个类，一个父类和一个从父类继承的子类。在初始化子类时，我使用super()关键字调用父类的构造函数。然后，我尝试访问子方法中的父类变量。但是，当我尝试这样做时，我收到了这个错误：Cannot read property 'undefined'。为什么变量是未定义的？构造器没有像我期望的那样工作吗？
class Book {
constructor(title, author, chapters) {
this.title = title; //string
this.author = author; //string
this.chapters = chapters; //array of strings
}
getTitle() {
return this.title;
}
getAuthor() {
return this.author;
}
}
class Chapter extends Book {
constructor(title, author, chapters, numberPages, subject, time, chapterIndex) {
super(title, author, chapters);
this.numberPages = numberPages;
this.subject = subject;
this.time = time;
this.chapterIndex = chapterIndex;
}
getChapterText() {
return this.chapters[this.chapterIndex];
}
}
var chapterOne = new Chapter("title", "author", ["lorem ipsum...", "lorem ipsum...", "lorem ipsum..."], 42, "about lorem ipsum", "3:01", 0); //book_object is an array of everything the chapter constructor needs
console.log(chapterOne.getChapterText());
我还尝试使用super.chapters来访问父类变量，但只得到了这个错误：unexpected keyword super。
更新
也许使用${book_object}让我的问题太混乱了。此javascript作为JSP (java服务器页面)运行。因此，它是在提供服务之前被编译的。我更新了我的问题以减少混淆。
更新2
class Book {
constructor(title, author, chapters) {
this.title = title; //string
this.author = author; //string
this.chapters = chapters; //array of strings
}
getTitle() {
return this.title;
}
getAuthor() {
return this.author;
}
}
class Chapter extends Book {
constructor(title, author, chapters, numberPages, subject, time, chapterIndex) {
super(title, author, chapters);
this.numberPages = numberPages;
this.subject = subject;
this.time = time;
this.currentChapter = this.getChapterText(); //I forgot to include this line in my original question.
this.chapterIndex = chapterIndex;
}
getChapterText() {
return this.chapters[this.chapterIndex];
}
}
var chapterOne = new Chapter("title", "author", ["lorem ipsum...", "lorem ipsum...", "lorem ipsum..."], 42, "about lorem ipsum", "3:01", 0); //book_object is an array of everything the chapter constructor needs
console.log(chapterOne.currentChapter);
我刚刚意识到，在我的实际代码中(这个问题中的代码是基于我的实际代码)，我在子类构造函数中调用了我的子类方法，并且在该方法中，我试图访问我的父类变量。下面是其中的一个片段。原来我的问题一直都是这样的。有人愿意解释一下为什么会发生这种情况吗？
回答 1
Stack Overflow用户
发布于 2018-09-27 04:32:18
如果book_object是构造器所需的参数数组，则需要对其进行扩展。正确的语法是...variable，而不是${variable}。
var chapterOne = new Chapter(...book_object)页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/52525515
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