无法扩展此 JavaScript 对象

Question

我检查了一些有类似问题的问题，但无法解决我的问题 file.js:

'use strict'

function singlyLinkedList() {
  if (this ) {
    this.head = null
  }
}

singlyLinkedList.prototype.append = function(value) {
  let node = {
    data: value,
    next: null
  }
  if( !this.head ) {
    this.head = node
  } else {
    let pointer = this.head
    while( pointer ) {
      pointer = pointer.next
    }
    pointer.next = node
  }
}

我从 index.html:

<!DOCTYPE html>
<html>
  <head>
    <title> Test </title>
    <meta charset="UTF-8">
    <script src="file.js"></script>
  </head>
  <body>
    <script>
      let linkedList = singlyLinkedList()
      let integersArray = [1, 22, 333, 4444]
      integersArray.forEach(element => linkedList.append(element))

    </script>
  </body>
</html>

使用 Chrome 浏览器浏览此 HTML 文件并检查控制台，显示此错误消息：

Uncaught TypeError: Cannot read property 'append' of undefined

如何解决这个问题？

更新：

我遇到的第二个问题（也许是一个单独的问题？）是如果我写：

function singlyLinkedList() {
    this.head = null
}

我收到此错误消息：

Uncaught TypeError: Cannot set property 'head' of undefined

Answer 1

您需要注意的几件事，

使用 new 关键字创建 'singlyLinkedList'
你的 while 循环的终止条件不正确。应该是 while( pointer.next )

检查以下版本，

//create a `file.js` file and put this code inside that. running this code snippet on Whosebug util wont work as you need a separate `file.js`

'use strict';

function singlyLinkedList() {
    this.head = null;
}

singlyLinkedList.prototype.append = function(value) {
    let node = {
        data: value,
        next: null
    };
    if( !this.head ) {
        this.head = node
    } else {
        let pointer = this.head;
        while( pointer.next ) {  //check this
            pointer = pointer.next
        }
        pointer.next = node
    }
};

<!DOCTYPE html>
<html>
  <head>
    <title> Test </title>
    <meta charset="UTF-8">
    <script src="file.js"></script>
  </head>
  <body>
    <script>
        let linkedList = new singlyLinkedList(); // check this
        let integersArray = [1, 22, 333, 4444];
        integersArray.forEach(element => linkedList.append(element));
        console.log('linkedList: ', linkedList);

    </script>
  </body>
</html>

它会记录类似的内容，

而且我坚信您需要使用 new 关键字来创建 singlyLinkedList 函数的实例，因为您想要使用 prototype 概念的好处

无法扩展此 JavaScript 对象

Can not extend this JavaScript object

javascript

prototype

function

strict