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

This article mainly introduces in detail the relevant information of javascript image preview and upload, which has certain reference value. Interested friends can refer to the examples of

I have shared the specific code for js image preview and upload for your reference. The specific content is as follows

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; alt="JavaScript implements image preview and upload (compatible with IE) code sharing" >" +
           "<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;);
    }

   }

  };

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