JavaScript对象的长度（即关联数组） [英] Length of a JavaScript object (that is, associative array)

问题描述

如果我有一个JavaScript关联数组，说：

If I have a JavaScript associative array, say:

var myArray = new Object();
myArray["firstname"] = "Gareth";
myArray["lastname"] = "Simpson";
myArray["age"] = 21;

有一个内置的或公认的最佳实践方法获取此数组的长度？

Is there a built-in or accepted best practice way to get the length of this array?

JavaScript没有关联数组 - 它只有对象的其可以用作关联数组的概念的**

JavaScript does not have associative arrays -- it only has objects, which can be used as a notion of associative arrays.**

推荐答案

最强劲的答案（即捕获的你试图同时引起的错误最少要做什么的意图）将是：

The most robust answer (i.e. that captures the intent of what you're trying to do while causing the fewest bugs) would be:

Object.size = function(obj) {
    var size = 0, key;
    for (key in obj) {
        if (obj.hasOwnProperty(key)) size++;
    }
    return size;
};

// Get the size of an object
var size = Object.size(myArray);

有在JavaScript的一种习惯，你不添加东西到的Object.prototype 的，因为它可以打破在各个库枚举。添加方法对象通常是安全的，但。

There's a sort of convention in JavaScript that you don't add things to Object.prototype, because it can break enumerations in various libraries. Adding methods to Object is usually safe, though.

下面是一个更新为2016年和wides ES5的$ P $垫的部署和超越。对于IE9 +和所有其他现代ES5 +功能的浏览器，你可以使用 Object.keys （）因此，上述code只是变成了：

Here's an update as of 2016 and widespread deployment of ES5 and beyond. For IE9+ and all other modern ES5+ capable browsers, you can use Object.keys() so the above code just becomes:

var size = Object.keys(myObj).length;

这并不需要修改，​​因为 Object.keys任何现有的原型（）现在是内置的。

This doesn't have to modify any existing prototype since Object.keys() is now built in.

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