设置JavaScript对象的长度属性 [英] Set length property of JavaScript object

问题描述

假设我有一个JavaScript对象：

Let's say I have a JavaScript object:

function a(){
    var A = [];
    this.length = function(){
        return A.length;
    };
    this.add = function(x){
        A.push(x);
    };
    this.remove = function(){
        return A.pop();
    };
};

我可以像这样使用它：

var x = new a();
x.add(3);
x.add(4);
alert(x.length()); // 2
alert(x.remove()); // 4
alert(x.length()); // 1

我试图让 .length 不是函数，所以我可以像这样访问它： x.length ，但我没有运气让它工作。

I was trying to make .length not a function, so I could access it like this: x.length, but I've had no luck in getting this to work.

我试过这个，但输出 0 ，因为这是 A 的长度当时：

I tried this, but it outputs 0, because that's the length of A at the time:

function a(){
    var A = [];
    this.length = A.length;
    //rest of the function...
};

我也尝试了这个，它还输出 0 ：

I also tried this, and it also outputs 0:

function a(){
    var A = [];
    this.length = function(){
        return A.length;
    }();
    //rest of the function...
};

如何获得 x.length 到输出对象内部数组的正确长度？

How do I get x.length to output the correct length of the array inside in the object?

推荐答案

因为当你调用 a.length ，你正在返回一个函数。为了返回输出，你必须实际调用该函数，即： a.length（）。

Because when you call a.length, you're returning a function. In order to return the output you have to actually invoke the function, i.e.: a.length().

顺便说一句，如果你不想让length属性成为函数而是实际值，你需要修改你的对象以返回属性。

As an aside, if you don't want to have the length property be a function but the actual value, you will need to modify your object to return the property.

function a() {
  var A = [];
  this.length = 0;
  this.add = function(x) {
    A.push(x);
    this.length = A.length;
  };
  this.remove = function() {
    var removed = A.pop();
    this.length = A.length;
    return removed;
  };
};

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