JavaScript 遍历对象属性和原型(prototype)链

Question

MDN状态:

Also, when iterating over the properties of an object, every enumerable property that is on the prototype chain will be enumerated.

所以我尝试了这个:

var x = {a: "I am a"};
var z = Object.create(x);

for( i in z )
{
    console.dir( i );

    if( i == "hasOwnProperty" ) {
        console.log( 'found hasOwnProperty' );
    }
}

仅输出 a 但不输出 hasOwnProperty。为什么？

Answer 1

因为 Object.prototype.hasOwnProperty 是不可枚举的:

Object.getOwnPropertyDescriptor(Object.prototype, 'hasOwnProperty')
  .enumerable // false

因此，它不会被 for...in 循环迭代。