for(var memberName in ad)
{
  //Member Name: memberName
  //Member Value: ad[memberName]
}

成员是指成员属性，成员变量，你可以叫它>_>

上面的代码将返回EVERYTHING，包括toString… 如果你只想查看对象的原型是否被扩展:

var dummyObj = {};  
for(var memberName in ad)
{
  if(typeof(dummyObj[memberName]) == typeof(ad[memberName])) continue; //note A
  //Member Name: memberName
  //Member Value: ad[memberName]

}

注A:我们检查虚拟对象的成员是否与测试对象的成员具有相同的类型。如果它是一个扩展，dummyobject的成员类型应该是"undefined"

这个怎么样?

var obj = {},
var isEmpty = !obj;
var hasContent = !!obj

你可以使用内置的Object。方法获取对象上的键列表并测试其长度。

var x = {};
// some code where value of x changes and than you want to check whether it is null or some object with values

if(Object.keys(x).length){
 // Your code here if x has some properties  
}

for (var hasProperties in ad) break;
if (hasProperties)
    ... // ad has properties

如果你必须确保安全并检查对象原型(这些是由某些库添加的，默认情况下没有):

var hasProperties = false;
for (var x in ad) {
    if (ad.hasOwnProperty(x)) {
        hasProperties = true;
        break;
    }
}
if (hasProperties)
    ... // ad has properties

我不确定这是否是一个好方法，但我使用这个条件来检查对象是否有或没有任何属性。可以很容易地转化成一个函数。

const obj = {};
    
if(function(){for (key in obj){return true}return false}())
{
  //do something;
}
else
{
  //do something else;
}
    
//Condition could be shorted by e.g. function(){for(key in obj){return 1}return 0}()

ES6函数

/**
 * Returns true if an object is empty.
 * @param  {*} obj the object to test
 * @return {boolean} returns true if object is empty, otherwise returns false
 */
const pureObjectIsEmpty = obj => obj && obj.constructor === Object && Object.keys(obj).length === 0

例子:

let obj = "this is an object with String constructor"
console.log(pureObjectIsEmpty(obj)) // empty? true

obj = {}
console.log(pureObjectIsEmpty(obj)) // empty? true

obj = []
console.log(pureObjectIsEmpty(obj)) // empty? true

obj = [{prop:"value"}]
console.log(pureObjectIsEmpty(obj)) // empty? true

obj = {prop:"value"}
console.log(pureObjectIsEmpty(obj)) // empty? false