JS实现浏览上传文件的代码

<div >
      <iframe id="t_load" name="t_load" ></iframe>
      <form action="" method="post" enctype="multipart/form-data" name="form1" target="t_load">
        <input type='text' name='textfield' id='textfield'  />
        <input type='button' value='浏览...' style="display: inline-block;
 margin-bottom: 0;
 font-size: 14px;
 border-radius: 4px;
padding: 6px 12px;
 margin: 2px 2px;
 border: 1px solid #357ebd;
 background: #1b9ad5;
 color: #fff;" />
        <input type="file" name="file1" accept="image/jpeg, image/gif" id="file1" onchange="document.getElementById('textfield').value=this.value"  />
        <input type="button" name="button" onclick="mysubmit()" value="上传" style="display: inline-block;
 margin-bottom: 0;
 font-size: 14px;
 border-radius: 4px;
padding: 6px 12px;
 margin: 2px 2px;
 border: 1px solid #357ebd;
 background: #1b9ad5;
 color: #fff;">
      </form>
    </div>
    <div  id="res"></div>
    <script>
      function mysubmit() {
        var a = document.getElementById("textfield").value;
        if(a == "") {
          alert("请上传文件");
          return;
        }
        document.form1.submit();
        ajaxsend();
      }
      function ajaxsend() {
        var xmlHttp;
        if(window.ActiveXObject) {
          xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
        } else {
          xmlHttp = new XMLHttpRequest();
        }
        xmlHttp.open("post", "upload", true);
        xmlHttp.onreadystatechange = function() {
          xmlHttp.readyState;
          if(xmlHttp.readyState == 4) {
            res.innerHTML = "上传成功！";
            setTimeout(function() {
              res.innerHTML = "";
            }, 2000);
          } else {
            document.getElementById("res").style.display = "inline";
          }
        }
        xmlHttp.send();
        var obj = document.getElementById('textfield');
        obj.outerHTML = obj.outerHTML;
      }
    </script>