循环obj

obj = {
    a: 123,
    b: 321
}

obj[Symbol.iterator] = function () {
  let keys = Object.keys(obj)
  let len = keys.length
  let n = 0

  return {
    next: function() {
       if (n<len) {
        return {
          value:{key:keys[n],value: obj[keys[n++]]},
          done: false
        } 
      } else {
        return {
          done: true
        } 
      }
    }
  }
}

for (var attr of obj) {
  console.log(attr)
}
// {key: "a", value: 123}
// {key: "b", value: 321}