var that = this

      if (e.target.files[0]) {

        var file = e.target.files[0]

        var reader = new FileReader()

        reader.readAsDataURL(file)

        reader.onload = function() {

          img.src = this.result

        }

        var img = new Image,

          width = 1024, //image resize   压缩后的宽

          quality = 0.8, //image quality  压缩质量

          canvas = document.createElement("canvas"),

          drawer = canvas.getContext("2d");

        img.onload = function() {

          canvas.width = width;

          canvas.height = width * (img.height / img.width);

          drawer.drawImage(img, 0, 0, canvas.width, canvas.height);
          //上传到七牛云

          var base64 = canvas.toDataURL("image/jpeg", quality); // 这里就拿到了压缩后的base64图片

          var pic = base64.split(',')[1];

          var url = "http://upload-z2.qiniu.com/putb64/-1";

          var xhr = new XMLHttpRequest();

          xhr.onreadystatechange = function() {

            if (xhr.readyState == 4) {

              that.imgs.push(JSON.parse(xhr.responseText).data.key);

            }

          }

          xhr.open("POST", url, true);

          xhr.setRequestHeader("Content-Type", "application/octet-stream");

          xhr.setRequestHeader("Authorization", "UpToken " + ‘七牛云token’);

          xhr.send(pic);

          // 清空文件上传控件的值  不清理会出现选择同样的图片会无法触发input事件了

          e.target.value = null;

        }