Detailed example of JS implementation of uploading images and previewing them

//js本地图片预览，兼容ie[6-9]、火狐、Chrome17+、Opera11+、Maxthon3
  function PreviewImage(fileObj) {
    //创建dom元素
    var pPreviewId = 'pPreview_' + fileObj.name;
    var imgPreviewId = 'imgHeadPhoto_' + fileObj.name;
    var html=&#39;<p id="&#39;+pPreviewId+&#39;">&#39;+
          &#39;<img id="&#39;+imgPreviewId+&#39;" src="images/moren.jpg" style="width: 120px; height: 120px; border: solid 1px #d2e2e2;" />&#39;+
         &#39;</p>&#39;;
    $(&#39;#&#39;+pPreviewId).remove();
    $(fileObj).after(html);
    //进行限制
    var allowExtention = ".jpg,.bmp,.gif,.png"; //允许上传文件的后缀名document.getElementById("hfAllowPicSuffix").value;
    var extention = fileObj.value.substring(fileObj.value.lastIndexOf(".") + 1).toLowerCase();
    var browserVersion = window.navigator.userAgent.toUpperCase();
    if (allowExtention.indexOf(extention) > -1) {  //格式正确
      if (fileObj.files) {  //HTML5实现预览，兼容chrome、火狐7+等
        if (window.FileReader) {
          var reader = new FileReader();
          reader.onload = function (e) {
            document.getElementById(imgPreviewId).setAttribute("src", e.target.result);
          }
          reader.readAsDataURL(fileObj.files[0]);
        } else if (browserVersion.indexOf("SAFARI") > -1) {
          $(&#39;#&#39;+pPreviewId).remove();
          alert("不支持Safari6.0以下浏览器的图片预览!");
        }
      } else if (browserVersion.indexOf("MSIE") > -1) {
        if (browserVersion.indexOf("MSIE 6") > -1) {//ie6
          document.getElementById(imgPreviewId).setAttribute("src", fileObj.value);
        } else {//ie[7-9]
          fileObj.select();
          if (browserVersion.indexOf("MSIE 9") > -1)
            fileObj.blur(); //不加上document.selection.createRange().text在ie9会拒绝访问
          var newPreview = document.getElementById(pPreviewId + "New");
          if (newPreview == null) {
            newPreview = document.createElement("p");
            newPreview.setAttribute("id", pPreviewId + "New");
            newPreview.style.width = document.getElementById(imgPreviewId).width + "px";
            newPreview.style.height = document.getElementById(imgPreviewId).height + "px";
            newPreview.style.border = "solid 1px #d2e2e2";
          }
          newPreview.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=&#39;scale&#39;,src=&#39;" + document.selection.createRange().text + "&#39;)";
          var temppPreview = document.getElementById(pPreviewId);
          temppPreview.parentNode.insertBefore(newPreview, temppPreview);
          temppPreview.style.display = "none";
        }
      } else if (browserVersion.indexOf("FIREFOX") > -1) {//firefox
        var firefoxVersion = parseFloat(browserVersion.toLowerCase().match(/firefox\/([\d.]+)/)[1]);
        if (firefoxVersion < 7) {//firefox7以下版本
          document.getElementById(imgPreviewId).setAttribute("src", fileObj.files[0].getAsDataURL());
        } else {//firefox7.0+          
          document.getElementById(imgPreviewId).setAttribute("src", window.URL.createObjectURL(fileObj.files[0]));
        }
      } else {
        document.getElementById(imgPreviewId).setAttribute("src", fileObj.value);
      }
    } else {
      $(&#39;#&#39;+pPreviewId).remove();
      alert("仅支持" + allowExtention + "为后缀名的文件!");
      fileObj.value = ""; //清空选中文件
      if (browserVersion.indexOf("MSIE") > -1) {
        fileObj.select();
        document.selection.clear();
      }
      fileObj.outerHTML = fileObj.outerHTML;
    }
    return fileObj.value;  //返回路径
  }