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）)