在这里提供解决方案 https://jsfiddle.net/mou882tw/

var data = [];
var lastMonth = "";

var child = document.getElementsByTagName('tr');
var temp = {};
var th = child[0].children;
for(var i=1; i<child.length; i++){
  var td = child[i].children;
  if(lastMonth != td[0].textContent){
  	if( JSON.stringify(temp) != '{}')
  		data.push(temp);
  	temp = {};
  	temp["Information"] = [];
  }

  var innerJSON = {};
  for(var j=0; j<td.length; j++){
  	if(j == 0){
    	temp[th[j].textContent] = td[j].textContent;
      lastMonth = td[j].textContent;
    } else {
    	innerJSON[th[j].textContent] = td[j].textContent;
    }
  }
  temp["Information"].push(innerJSON);
  if(i == (child.length -1)){
  	data.push(temp);
  }
}
console.log(data);

<table>
  <thead>
    <tr>
      <th>Month</th>
      <th>Name</th>
      <th>Sum</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>January</td>
      <td>John</td>
      <td>25</td>
    </tr>
    <tr>
      <td>February</td>
      <td>Jane</td>
      <td>30</td>
    </tr>
    <tr>
      <td>February</td>
      <td>John</td>
      <td>35</td>
    </tr>
    <tr>
      <td>February</td>
      <td>Alex</td>
      <td>20</td>
    </tr>
    <tr>
      <td>March</td>
      <td>Jane</td>
      <td>32</td>
    </tr>
    <tr>
      <td>March</td>
      <td>John</td>
      <td>35</td>
    </tr>
    <tr>
      <td>March</td>
      <td>Alex</td>
      <td>30</td>
    </tr>
  </tbody>
</table>

希望这会帮助您。