將類似於 info 格式轉化為 info2 

    var info = {
      id: 1,
      id1: 2,
      userName1: '劉玄德',
      userName2: '劉玄德',
      userName3: '大哥',
      userAge: 45,
      userAge1: 46,
      userAge2: 47
    }

    var info2 = {
      id: 1,
      id_1: 2,
      user_name_1: '劉玄德',
      user_name_2: '劉玄德',
      user_name_3: '劉玄德',
      user_age: 45,
      user_age_1: 46,
      user_age_2: 47
    }
 

下屬兩種解決方案：可謂相當瀟灑的答案，一行搞定

// segmentDefault回答者 asseek 的答案： 
const toLine = hump => hump.replace(/([A-Z]|\d)/g, (a, l) => `_${l.toLowerCase()}`);

var info = {
  id: 1,
  id1: 2,
  userName1: '劉玄德',
  userName2: '劉玄德',
  userName3: '大哥',
  userAge: 45,
  userAge1: 46,
  userAge2: 47
};
var newObj = {}
for (let k in info) {
  newObj[toLine(k)] = info[k]
}
console.log(newObj)
 

本人的答案，想了很久，asseek 的答案可謂是天上飛，我的答案就是地上爬了

<script>
    var info = {
      id: 1,
      id1: 2,
      userName1: '劉玄德',
      userName2: '劉玄德',
      userName3: '大哥',
      userAge: 45,
      userAge1: 46,
      userAge2: 47
    }

    var info2 = {
      id: 1,
      id_1: 2,
      user_name_1: '劉玄德',
      user_name_2: '劉玄德',
      user_name_3: '劉玄德',
      user_age: 45,
      user_age_1: 46,
      user_age_2: 47
    }

    function copy(obj){//用於複製一個物件
      var newobj = {};
      for ( var attr in obj) {
          newobj[attr] = obj[attr];
      }
      return newobj;
    }
    var changeObj = function (obj) {
      var copyobj = copy(obj)
      var regNum = new RegExp(/\d/)
      var regStr = new RegExp(/[A-Z]/g)
      var arr = Object.keys(obj);

      var newObj = {}
      arr.forEach((k, index) => {
        var kArr = k.split('')
        var newK = ''
        kArr.forEach((item,index)=>{
          if(regNum.test(item)){
            kArr[index] = "_" + item
          }
          if(regStr.test(item)){
            kArr[index] = "_" + item.toLowerCase()
          }
        })
        newKey = kArr.join('')
        newObj[newKey] = obj[k]
        console.log(newKey)
        
      })
      console.log(newObj)
      return newObj
    }
    changeObj(info)
  </script>