JavaScript implements image preview and upload (compatible with IE) code sharing

var dailiApply = {

   change: function (evt) {
    evt.preventDefault();
    var pic = document.getElementById("preview"),
     file = document.getElementById("f");

    var ext=file.value.substring(file.value.lastIndexOf(".")+1).toLowerCase();
    // gif在IE浏览器暂时无法显示
    if(ext!='png'&&ext!='jpg'&&ext!='jpeg'){
     alert("图片的格式必须为png或者jpg或者jpeg格式！");
     return;
    }
    var isIE = navigator.userAgent.match(/MSIE/)!= null,
     isIE6 = navigator.userAgent.match(/MSIE 6.0/)!= null;

    if(isIE) {
     file.select();
     var reallocalpath = document.selection.createRange().text;

     // IE6浏览器设置img的src为本地路径可以直接显示图片
     if (isIE6) {
      pic.src = reallocalpath;
     }else {
      // 非IE6版本的IE由于安全问题直接设置img的src无法显示本地图片，但是可以通过滤镜来实现
      pic.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod='image',src=\"" + reallocalpath + "\")";
      // 设置img的src为base64编码的透明图片 取消显示浏览器默认图片
      pic.src = 'data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==';
     }
    }else {
     var file_arr = file.files;
     var ul = $(".weui_uploader_files");
     if(file_arr.length < 7) {
      for(var key in file_arr) {
       if(file_arr.hasOwnProperty(key)) {
        var f = file_arr[key];
        var url = URL.createObjectURL(f);
        var reader = new FileReader();
        console.log(f);
        reader.readAsDataURL(f);
        n +=1;
        if(n < 7) {
         reader._onload = function(e) {

          // 拼接显示预览图片的html
          var list = $("<li class=&#39;weui_uploader_file&#39; style=&#39;position: relative&#39;>" +
           "<img id=&#39;preview" + n + "&#39; class=preview_li&#39; style=&#39;width: 100%;height: 100%&#39;>" +
           "<span id=&#39;delImg" + n+ "&#39; style=&#39;position: absolute; top: 0; right: 4px; color: #e4007f&#39;>X</span></li>");
          ul.append(list);
          // 将转化后的图片地址放在img中
          var pic = document.getElementById(&#39;preview&#39; + n);
          //pic.src = this.result;
          pic.src=url;
          dailiApply.compress(f, .7,undefined);
          //images.push(f);
          document.getElementById(&#39;delImg&#39; + n).addEventListener("click", function () {
           $(this).parent().remove();
           --n;
          });

         };
         reader._onload();
        }else {
         $.alert("最多上传6张图片");
         n = 6;
        }
       }
      }
     }else {
      $.alert("最多上传6张图片");
     }
    }
    return false;
   },
   /**
    * @param {Object} f input选择的图片 必填
    * @param {String} quality  图片压缩的质量[0, 1]
    * @param {String} output_img_type  输出图片的类型
    */
   compress: function (f, quality, output_img_type) {
    var mime_type = "image/jpeg";
    if(output_img_type!=undefined && output_img_type=="image/png"){
     mime_type = "image/png";
    }
    createImageBitmap(f).then(function(imageBitmap) {
     var max = 1000; // 设置最大分辨率
     var c_w = &#39;&#39;;
     var c_h = &#39;&#39;;
     var width = imageBitmap.width;
     var height = imageBitmap.height;
     // 等比例缩放
     if (width > max || height > max) {
      if (width > height) {
       c_w = max;
       c_h = max * height / width;
      } else {
       c_h = max;
       c_w = max * width / height;
      }
     }else {  // 不缩放
      c_w = width;
      c_h = height;
     }

     var canvas = document.createElement(&#39;canvas&#39;);
     canvas.width = c_w;
     canvas.height = c_h;
     var ctx = canvas.getContext(&#39;2d&#39;);
     ctx.drawImage(imageBitmap,0,0, width, height, 0, 0, c_w, c_h);
     canvas.toBlob(function(blob){
      images.push(blob);
     },mime_type, quality);
    });
   },
   submit: function () {
    var content = $(".weui_textarea").val().trim();
    var xhr = new XMLHttpRequest();
    var fd = new FormData(document.getElementById(&#39;uploadForm&#39;));
    $.each(images,function(i,e){
     fd.append("images", e);
    });
    fd.append("remark", content);
    fd.append("substationproxyId", 8);
    console.log(images);
    console.log(fd);
    if(content) {
     $.ajax({
      url: CONFIG.API.addSubProxyRecruit,
      type: "POST",
      data: fd,

      processData: false, // tell jQuery not to process the data
      contentType: false, // tell jQuery not to set contentType
      beforeSend: function (xhr) {
       $.showLoading();
       $(this).prop("disabled", true)
      },
      success: function (json) {
       console.log(json);
       $.hideLoading();
       $(this).prop("disabled", false);
       if(json.errorCode == 0) {
        $.alert("保存成功", function () {
         location.reload();
        })
       }else if(json.errorCode == "-101") {
        $.alert(&#39;出错：&#39; +json.message, function () {
         location.href = CONFIG.HTML.login;
        });
       }else {
        $.alert(json.message, function () {

        })
       }
      }
     });
    }else {
     $.alert(&#39;请输入内容&#39;);
    }

   }

  };