Javascript 帮助 : Functions/Objects

Question

因此，使用 Code Academy，我在 Javascript 教程的“对象”部分，我真的很难全神贯注于函数和对象。我想要一些帮助并用下面的部分代码进行解释。我在每一行上都评论了我需要帮助的内容。非常感谢。

// Obviously declaring the Rabbit function with adjective to be called

function Rabbit(adjective) { 

  // I don't understand this line, or the context of why this is being used.

  this.adjective = adjective; 

  // Why declare another function here? Is a function within a function 
  // considered a Method or is that only Function within an Object?

  this.describeMyself = function() { 

    // I get this part but why does it need a function to do this?

    console.log("I am a " + this.adjective + " rabbit"); 
  };
}

// I don't get this either, Isn't this declaring a new object? How can   
// that be when you only have a Function named Rabbit?

var rabbit1 = new Rabbit("fluffy"); 
var rabbit2 = new Rabbit("happy");
var rabbit3 = new Rabbit("sleepy");

// How could this work if describeMyself is in the Rabbit function and 
// has nothing to do with rabit1?

console.log(rabbit1.describeMyself); 
console.log(rabbit2.describeMyself);
console.log(rabbit3.describeMyself);

希望不要太困惑，但如果你们中任何更有经验的 Javascript 人可以友好地解释我在评论中谈到的一切，我将不胜感激。谢谢

Answer 1

1. Rabbit 是一个构造函数，当使用 new 关键字调用时，它会生成一个实例。
2. 当您这样做时，this 指向您创建的实例。

因此，通过 var rabbit1 = new Rabbit('fluffy')，您创建了一个看起来像这样的对象并将其分配给变量 rabbit1:

{
  adjective: 'fluffy',
  describeMyself: function() {...}
}

由于 rabbit1.describeMyself 中的 this 指向实例本身 (rabbit1)，当您调用 rabbit1.describeMyself() ，this.adjective 实际上给你 rabbit1.adjective。这就是为什么您会得到 'fluffy' 的原因。

对于rabbit2和rabbit3，this分别指向它们自己。