为什么我不能在Set.prototype中使用for ... in循环？ [重复]

I want to go through all the functions in the Set.prototype.

For...in doesn't do it.

var proto = Set.prototype;
for (var p in proto) {
  console.log(p);
}
// does ABSOLUTELY NOTHING

所以我的问题分为两部分：

1: Why does it not work?

2: How can I go through all the Set.prototype functions?