对象是空的吗？

我假设用 空 表示“没有任何属性”。

// Speed up calls to hasOwnPropertyvar hasOwnProperty = Object.prototype.hasOwnProperty;function isEmpty(obj) {    // null and undefined are "empty"    if (obj == null) return true;    // Assume if it has a length property with a non-zero value    // that that property is correct.    if (obj.length > 0)    return false;    if (obj.length === 0)  return true;    // If it isn't an object at this point    // it is empty, but it can't be anything *but* empty    // Is it empty?  Depends on your application.    if (typeof obj !== "object") return true;    // Otherwise, does it have any properties of its own?    // Note that this doesn't handle    // toString and valueOf enumeration bugs in IE < 9    for (var key in obj) {        if (hasOwnProperty.call(obj, key)) return false;    }    return true;}

例子：

isEmpty(""), // trueisEmpty(33), // true (arguably could be a TypeError)isEmpty([]), // trueisEmpty({}), // trueisEmpty({length: 0, custom_property: []}), // trueisEmpty("Hello"), // falseisEmpty([1,2,3]), // falseisEmpty({test: 1}), // falseisEmpty({length: 3, custom_property: [1,2,3]}) // false

如果只需要处理ECMAscript5浏览器，则可以使用

Object.getOwnPropertyNames

hasOwnProperty

if (Object.getOwnPropertyNames(obj).length > 0) return false;

这将确保即使对象仅具有不可枚举的属性，

isEmpty