Javascript - 继承和修改对象

Question

我正在尝试像这样更改对象的属性：

secondFunction = function()
{
    var bla = { 
    a:1, //properties
    };

    bla.localFunction = function(){
    a = 2; //can he read and modify this property?
    }

return bla; //return back object
}

firstFunction = function()
{
var testing = secondFunction(); //now testing is the object.
testing.localFunction(); //this is supposed to call localFunction and change the "a" property to 2
console.log(testing.a); //displays 1, not 2 as I thought it would
}

firstFunction(); 

我可能是错的（因为我是 javascript 新手），但是属性对于整个对象是全局的，并且由于 localFunction 是对象的一部分，我认为它应该能够读取属性“a”并对其进行修改到 2. 我哪里错了？

Answer 1

让我给你一个指向 MDN 上 this 文档的链接，他们在解释方面做得比我在这里做得更好：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this

这是你的函数的一个工作实现，唯一的区别是我使用了document.write，所以 sn-p 立即吐出响应，应该是12。

secondFunction = function()
{
    var bla = { 
        a:1,
    };

    bla.localFunction = function(){
        // Heres the magic: this is currently bound to your `bla` object inside this function!
        this.a = 2;
    }

    return bla;
}

firstFunction = function(){
    var testing = secondFunction();
    document.write(testing.a);
    testing.localFunction();
    document.write(testing.a);
}

firstFunction(); 

这是一个更干净的 sn-p 版本：

function secondFunction(){
  // Dont waste precious memory to store something you could do in one go!
  return { 
    a: 1,
    // Functions are first-class in JS, so you can simply use them as values
    localFunction: function(){
      this.a = 2;
    }
  };
}

function firstFunction(){
  var testing = secondFunction();
  document.write(testing.a);
  testing.localFunction();
  document.write(testing.a);
}

firstFunction();