javascript - Javascript For循环自动增量不起作用

Question

我正在尝试在 JavaScript 中运行 For 循环，但它对我不起作用。自动增量值不起作用我试图通过更改来检查：

alert('add_fname_'+i);

但它"add_fname_0"作为输出给出

function checkadditionals(){
    var tvrs = Number(document.getElementById('additional_travellers').value);

    for ( var i = 0; i < tvrs; i++) {
      console.log('add_fname_' + i);
      document.getElementById('add_fname_'+i).required = true;
      document.getElementById('add_lname_'+i).required = true;
      document.getElementById('add_dob_'+i).required = true;
      document.getElementById('relation_'+i).required = true;
      document.getElementById('pre_exe_'+i).required = true;
    }
}

<select onchange="checkadditionals()" class="form-control" id="additional_travellers" name="additional_travellers">
  <option value="0">None</option> 
  <option value="1">1</option>
  <option value="2">2</option>
  <option value="3">3</option>
  <option value="4">4</option> 
  <option value="5">5</option>
  <option value="6">6</option>
  <option value="7">7</option>
  <option value="8">8</option>
  <option value="9">9</option>
</select>

标签： javascriptfor-loop