Codecademy Javascript 'this' and Solution

Question

我正在尝试学习JavaScript bij遵循codecademy.com的课程，但我似乎无法理解'this'关键字。我还需要改变矩形的宽度和高度的属性。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?另外，错误信息告诉我，我没有定义settwidth…

请把"this"也解释一下

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，你要做的，你只需要这样做:

// 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，脚本没有得到上面的代码，因为这部分

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

导致问题，因为setWidth和setHeight是对不存在的变量的引用，所以你会得到Uncaught ReferenceError: setWidth is not defined(…)错误。这部分实际上是不需要的，所以只需删除它，它应该可以正常工作。

JavaScript中有大量关于this的资源。从MDN开始