<div>
  <input type="text" placeholder="用户名">
  <input type="text" placeholder="用户名">
  <input type="text" type="hidden">
  <input type="text" type="hidden">
  <a class="reduce" onclick="less()">—</a>
 </div>

.reduce{
   display: inline-block;
   color: white;
   text-align: center;
   width: 30px;
   height: 30px;
   background: red;
   line-height: 30px;
   cursor: pointer;
  }
  input{
   height: 18px;
   padding: 5px 10px;
  }

<script src="jquery-1.7.2.min.js"></script>
<script>
 var Reduce = document.getElementsByClassName("reduce");
 var Inp = document.getElementsByTagName("input");
 function less(){
    //查找元素的上一个元素 并移除
  $(".reduce").prev().remove();
  if(Inp.length < 1){
   $(".reduce").remove()
  }
 }
 $(".reduce")
</script>