2019-08-16 node各种小功能函数

1.返回指定在obj中返回指定key得对象，
keys可以是字符串，各个key值以空格分隔

function(obj, keys){
  obj = obj || {};
  if ('string' == typeof keys) keys = keys.split(/ +/);
  return keys.reduce(function(ret, key){
    if (null == obj[key]) return ret;
    ret[key] = obj[key];
    return ret;
  }, {});
};