運用in運算子來穫取未知對象屬性以及屬性值

var obj = new Object();
 obj.attr1="1111"
 obj.attr2="2222"
 alert(obj.attr1);
 alert(obj.attr2);
 for(attribute in obj){

  var attrName = attribute;//屬性名稱
  alert(attrName);

  var value = null;
  eval("value=o."+attrName);//屬性值
  alert(value);

 }
用in運算子判斷物件是否有此屬性

console.log(attr in obj);