Javascript：array.length返回undefined [英] Javascript : array.length returns undefined

问题描述

我有一组由PHP的 json_encode 函数传递的数据。我正在使用jQuery getJSON 函数对其进行解码：

I have a set of data that is being passed on by the PHP's json_encode function. I'm using the jQuery getJSON function to decode it:

$.getJSON("url", function (data) {
    console.log(data);
});

控制台中的输出如下所示：

The output looks like this in the console:

Object {1: Object, 2: Object, 3: Object, 4: Object, 5: Object, 6: Object, 7: Object, 8: Object, 9: Object, 10: Object}

我可以使用数据访问每个数组[1] ， data [2] 等，但是为了让它更容易我想到循环，所以我可以一次访问所有：

I can access each array by using data[1], data[2] etc, but to make it easier I thought of looping thought it so I can access all at once:

$.getJSON("url", function (data) {
    for (var i = 0, len = data.length; i < len; i++) {
        //do something
    }
});

但是我无法使用它，因为 data.length 返回值 undefined 。有什么问题，如何解决？

However I can't get this to work because the data.length returns the value undefined. What is wrong and how can I fix it?

推荐答案

对象没有 .length property。

Objects don't have a .length property.

一个简单的解决方案，如果你知道你不必担心 hasOwnProperty 检查，就是这样做：

A simple solution if you know you don't have to worry about hasOwnProperty checks, would be to do this:

Object.keys(data).length;

如果 支持IE 8或更低版本，你将拥有改为使用循环：

If you have to support IE 8 or lower, you'll have to use a loop, instead:

var length= 0;
for(var key in data) {
    if(data.hasOwnProperty(key)){
        length++;
    }
}

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