javascript - 如何获取对象长度[重复](How to get object length [duplicate])

Question

This question already has an answer here:

(这个问题在这里已有答案：)

• Length of a JavaScript object 38 answers

  (JavaScript对象的长度 38回答)

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

(是否有任何可以返回对象长度的内置函数？)

For example, I have a = { 'a':1,'b':2,'c':3 } which should return 3 .

(例如，我有a = { 'a':1,'b':2,'c':3 }应返回3 。)

If I use a.length it returns undefined .

(如果我使用a.length则返回undefined 。)

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

(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？)

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.

(有一个相关的问题（ JSON对象的长度 ） - 在选择的答案中，用户建议将对象转换为数组，这对我的任务来说不太舒服。)

  ask by Larry Cinnabar translate from so

Answer 1

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

(对于支持Object.keys（）的浏览器，您只需执行以下操作：)

Object.keys(a).length;

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

(否则（特别是在IE <9中），您可以使用for (x in y)循环自行遍历对象：)

var count = 0;
var i;

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

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.

(hasOwnProperty用于确保您只计算来自对象文字的属性，而不是它从其原型“继承”的属性。)