如何获取JavaScript对象中的字段数？ [英] How do I get number of fields in JavaScript object?

问题描述

我正在尝试将JavaScript对象用作关联数组，一切都很顺利，直到我需要获取存储在其中的条目数。最简单，最优雅的方法是什么？我能想到的是为每个循环或jQuery $。每个函数运行，看看它有多少次迭代会这样做但看起来很糟糕。

I'm trying to use JavaScript object as an associative array and everything was well until I needed to get number of entries that are stored in it. What is the easiest and most elegant way to do that? All I can think of is to run for each loop or jQuery $.each function and just see how much iterations it would do but that looks like an an awful thing to do.

推荐答案

旧的Firefox支持 __ count __ property。较新的环境支持ES5的 Object.keys 。对于较旧的环境，我们必须回退到迭代对象并手动计数（呃！）：

Old Firefox supports the __count__ property. Newer environments support ES5's Object.keys. For older environments we have to fallback to just iterating over the object and counting manually (ugh!):

function count(obj) {

    if (obj.__count__ !== undefined) { // Old FF
        return obj.__count__;
    }

    if (Object.keys) { // ES5 
        return Object.keys(obj).length;
    }

    // Everything else:

    var c = 0, p;
    for (p in obj) {
        if (obj.hasOwnProperty(p)) {
            c += 1;
        }
    }

    return c;

}

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