javascript - 如何有效地计算JavaScript中对象的键/属性数量？(How to efficiently count the number of keys/properties of an object in JavaScript?)

Question

What's the fastest way to count the number of keys/properties of an object?

(计算对象的键/属性数的最快方法是什么？)

It it possible to do this without iterating over the object?

(是否可以在不迭代对象的情况下执行此操作？)

ie without doing

(即不做)

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

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

(（Firefox确实提供了一个神奇的__count__属性，但此属性已在版本4的某个位置删除。）)

  ask by mjs translate from so

Answer 1

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

(要在任何与ES5兼容的环境 （例如Node ，Chrome，IE 9+，Firefox 4+或Safari 5+）中执行此操作：)

Object.keys(obj).length

• Browser compatibility

  (浏览器兼容性)

• Object.keys documentation (includes a method you can add to non-ES5 browsers)

  (Object.keys文档 （包括可以添加到非ES5浏览器的方法）)