JS - 遍歷對象屬性

栗子：

var obj = {
  "name": "Poly",
  "career": "it"
}
Object.defineProperty(
obj, "age", 
{ value:"forever 18", enumerable:false }
);
Object.prototype.protoPer1 = function(){console.log("proto");};
Object.prototype.protoPer2 = 2;

for in

用於遍歷對象的可枚舉屬性，包括自有屬性、繼承自原型的屬性

for(var a in obj){
  console.log(a);
}
//輸出：name, career, protoPer1, protoPer2

Object.keys

返回一個數組，元素均為對象自有的可枚舉屬性

console.log(Object.keys(obj));
//輸出：["name", "career"]

Object.getOwnProperty

用於返回對象的自有屬性，包括可枚舉和不可枚舉的

console.log(Object.getOwnPropertyNames(obj));
//輸出：["name", "career", "age"]