prototype 1.6.0.3 源码阅读中遇到的问题

[code="javascript"]
Class.Methods = {
addMethods: function(source) {
var ancestor = this.superclass && this.superclass.prototype;
var properties = Object.keys(source);
//下面这两句是干什么用的？貌似永远都走不到啊！Object.keys({ toString: true }).length永远等于1啊！
//跑不到的代码还要写上来，不理解中。往指点！我第一次看prototype源码
if (!Object.keys({ toString: true }).length)
properties.push("toString", "valueOf");

for (var i = 0, length = properties.length; i < length; i++) {
  var property = properties[i], value = source[property];
  if (ancestor && Object.isFunction(value) &&
      value.argumentNames().first() == "$super") {
    var method = value;
    value = (function(m) {
      return function() { return ancestor[m].apply(this, arguments) };
    })(property).wrap(method);

    value.valueOf = method.valueOf.bind(method);
    value.toString = method.toString.bind(method);
  }
  this.prototype[property] = value;
}

return this;

}
};
[/code]

Object.keys({ toString: true }).length这个不一定是1哦，
万一有人用了delete把它删除了，这句就有用了