//压缩base64方法
    dealImage(base64, w = 100000) {
      var preview = document.getElementById("uploadimg");
      var newImage = new Image();
      var quality = 0.6; //压缩系数0-1之间
      newImage.src = base64;
      newImage.setAttribute("crossOrigin", "Anonymous"); //url为外域时需要
      var imgWidth, imgHeight;
      var that = this;
      newImage.onload = function () {
        imgWidth = this.width;
        imgHeight = this.height;
        var canvas = document.createElement("canvas");
        var ctx = canvas.getContext("2d");
        if (Math.max(imgWidth, imgHeight) > w) {
          if (imgWidth > imgHeight) {
            canvas.width = w;
            canvas.height = (w * imgHeight) / imgWidth;
          } else {
            canvas.height = w;
            canvas.width = (w * imgWidth) / imgHeight;
          }
        } else {
          canvas.