如何获取对象长度 [英] How to get object length

问题描述

有没有可以返回对象长度的内置函数?

Is there any built-in function that can return the length of an object?

例如，我有 a = { 'a':1,'b':2,'c':3 } 应该返回 3.如果我使用 a.length 它返回 undefined.

For example, I have a = { 'a':1,'b':2,'c':3 } which should return 3. If I use a.length it returns undefined.

它可能是一个简单的循环函数，但我想知道是否有内置函数?

It could be a simple loop function, but I'd like to know if there's a built-in function?

有一个相关的问题(JSON 对象的长度)——在用户建议将对象转换为数组的所选答案，这对我的任务来说不太合适.

There is a related question (Length of a JSON object) - in the chosen answer the user advises to transform object into an array, which is not pretty comfortable for my task.

推荐答案

对于支持 Object.keys() 你可以简单地做:

For browsers supporting Object.keys() you can simply do:

Object.keys(a).length;

否则(尤其是在 IE < 9 中)，您可以自己使用 for (x in y) 循环遍历对象:

Otherwise (notably in IE < 9), you can loop through the object yourself with a for (x in y) loop:

var count = 0;
var i;

for (i in a) {
    if (a.hasOwnProperty(i)) {
        count++;
    }
}

hasOwnProperty 用于确保您只计算对象字面量中的属性，而不是它从其原型继承"的属性.

The hasOwnProperty is there to make sure that you're only counting properties from the object literal, and not properties it "inherits" from its prototype.

这篇关于如何获取对象长度的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！