Question

我正在尝试在codecademy.com上学习JavaScript bij，但我似乎无法理解'this'关键字。另外，我需要更改矩形的属性宽度和高度。这是开始：

    var rectangle = new Object();
    rectangle.height = 3;
    rectangle.width = 4;
    // here is our method to set the height
    rectangle.setHeight = function (newHeight) {
      this.height = newHeight;
    };
    // help by finishing this method
    rectangle.setWidth =


    // here change the width to 8 and height to 6 using our new methods

目前我有：

    var rectangle = new Object();
    rectangle.height = 3;
    rectangle.width = 4;

    rectangle.setHeight = function (newHeight) {
      this.height = newHeight;
    };
    rectangle.setWidth = function (newWidth) {
      this.width = newWidth;
    };

    rectangle.setWidth = setWidth;
    rectangle.setHeight = setHeight;
    rectangle.setWidth(8);
    rectangle.setHeight(6);

我做错了什么？此外，错误消息告诉我，我没有定义setWidth ...

请解释'这个'。

Answer 1

这部分是正确的：

rectangle.setHeight = function (newHeight) {
  // `this` here is not set yet when declaring functions
  // it will be set when the function will be executed
  this.height = newHeight;
};
rectangle.setWidth = function (newWidth) {
  this.width = newWidth;
};

然后去做，你正在尝试做的只需要这样做：

// since these two methods are going to be called as methods of `rectangle` object
// `this` inside these functions will be set to reference `rectangle` object
rectangle.setWidth(8);
rectangle.setHeight(6);

然而，脚本没有达到上面的代码，因为这部分

rectangle.setWidth = setWidth;
rectangle.setHeight = setHeight;

会导致问题，因为setWidth和setHeight是对不存在的变量的引用，因此您会收到Uncaught ReferenceError: setWidth is not defined(…)错误。而这部分实际上并不需要，所以只需删除它就可以正常工作。

JavaScript中this上有大量资源。从MDN开始。

Codecademy Javascript'this'和解决方案

1 个答案: