JavaScript：获取对象的第一个也是唯一的属性名称 [英] JavaScript: Get first and only property name of object

问题描述

如果我想枚举对象的属性并想要忽略原型，我会使用：

If I want to enumerate the properties of an object and want to ignore prototypes, I would use:

var instance = { ... };

for (var prop in instance) {
    if (instance.hasOwnProperty(prop)) {
        ... 
    }
}

如果实例只有一个属性，我想要什么获得该属性名称？有没有比这样做更简单的方法：

What if instance only has one property, and I want to get that property name? Is there an easier way than doing this:

var instance = { id: "foobar" };

var singleMember = (function() {
    for (var prop in instance) {
        if (instance.hasOwnProperty(prop)) {
            return prop;
        }
    }
})();

推荐答案

也许 Object.keys 可以为您服务。如果其长度返回1，则可以使用 yourObject [Objects.keys [0]] 来获取对象的唯一属性。 MDN-link还显示了一个自定义函数，用于没有键方法 ¹ 的环境。代码如下：

Maybe Object.keys can work for you. If its length returns 1, you can use yourObject[Objects.keys[0]] to get the only property of the object. The MDN-link also shows a custom function for use in environments without the keys method¹. Code like this:

var obj = {foo:'bar'}, 
    kyz = Object.keys(obj);
if (kyz.length === 1){
   alert(obj[kyz[0]]); //=> 'bar'
} else {
  /* loop through obj */
}

¹ 某些旧版浏览器不支持 Object.keys 。 MDN链接提供代码以使其在这些浏览器中工作。请参阅上述 MDN页中的标题兼容性

¹ Some older browsers don't support Object.keys. The MDN link supplies code to to make it work in these browsers too. See header Compatibility in the aforementioned MDN page

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