!DOCTYPE html>
html lang="en">
head>
  meta charset="UTF-8">
  title>Document/title>
  script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js">/script>
  style type="text/css">
    body{
      margin:0;
      padding: 0;
    }
    form{
      width: 500px;
      margin:40px auto;
    }
    .search-wrap{
      position: relative;
    }
    li{
      padding: 0;
      padding-left: 10px;
      list-style: none;
    }
    li:hover{
      background-color: #ccc;
      color: #fff;
      cursor: pointer;
    }
    #xiala{
      position: absolute;
      top: 40px;
      left: 0;
      background-color: #c2c2c2;
      width: 200px;
      margin:0;
      padding: 0 ;
      display: none;
    }
  /style>
/head>
body>
  form action="">
    div class="search-wrap">
      input type="text" id="search">
      ul id="xiala">
      /ul>
      input type="button" value="go" id="sousuo">
      div id="searVal" style="display:inline-block;border:1px solid #ccc">/div>
    /div>
  /form>
/body>
script type="text/javascript">
  var search=$("#search");
  search.on("input",function(){  //输入框内容改变发请求
    $.ajax({
      url:'a.txt',
      type:'GET',
      async:true,
      data:{value:$("#search").val()},
      success:function(data){
        var arr=data.split(',');
        console.log(arr);
        $("#xiala").html("");
        $.each(arr,function(i,n){
          var oLi=$("li>"+arr[i]+"/li>");
          $("#xiala").append(oLi);
          $("#xiala").css("display","block");
        })
      }
    });
    $("#xiala").css("display","block");       //内容改变下拉框显示
    $("#searVal").html(search.val())
  })
  function stopPropagation(e) {
    if (e.stopPropagation){
       e.stopPropagation();
    }else{
     e.cancelBubble = true;
    }
  }
  $(document).on('click',function(){     //点击页面的时候下拉框隐藏
    $("#xiala").css("display","none");
  });
  $(document).on("click","#xiala li",function(){ //点击下拉框选项的时候改变输入框的值
    search.val($(this).text());
    $("#searVal").html($(this).text());
    $("#xiala").css("display","none");
  })
/script>
/html>

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