如何有效地计算 JavaScript 中对象的键/属性的数量 [英] How to efficiently count the number of keys/properties of an object in JavaScript

问题描述

计算对象的键/属性数量的最快方法是什么?是否可以在不迭代对象的情况下执行此操作?即，不做:

What's the fastest way to count the number of keys/properties of an object? Is it possible to do this without iterating over the object? I.e., without doing:

var count = 0;
for (k in myobj) if (myobj.hasOwnProperty(k)) ++count;

(Firefox 确实提供了一个神奇的 __count__ 属性，但它在版本 4 左右的某个地方被删除了.)

(Firefox did provide a magic __count__ property, but this was removed somewhere around version 4.)

推荐答案

要在任何ES5 兼容环境，例如 Node.js、Chrome、Internet Explorer 9+、Firefox 4+ 或 Safari 5+:

To do this in any ES5-compatible environment, such as Node.js, Chrome, Internet Explorer 9+, Firefox 4+, or Safari 5+:

Object.keys(obj).length

• 浏览器兼容性
• Object.keys 文档(包括可以添加到非 ES5 浏览器的方法)
• Browser compatibility
• Object.keys documentation (includes a method you can add to non-ES5 browsers)

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