export function compress(fileObj, callback) {
  try {
    const image = new Image();
    image.src = URL.createObjectURL(fileObj);
    image.onload = function() {
      const that = this;
      // 默认按比例压缩
      let w = that.width;
      let h = that.height;
      const scale = w / h;
      w = fileObj.width || w;
      h = fileObj.height || w / scale;
      let quality = 0.7; // 默认图片质量为0.7
      // 生成canvas
      const canvas = document.createElement("canvas");
      const ctx = canvas.getContext("2d");
      // 创建属性节点
      const anw = document.createAttribute("width");
      anw.nodeValue = w;
      const anh = document.createAttribute("height");
      anh.nodeValue = h;
      canvas.setAttributeNode(anw);
      canvas.setAttributeNode(anh);
      ctx.drawImage(that, 0, 0, w, h);
      // 图像质量
      if (fileObj.quality && fileObj.quality <= 1 && fileObj.quality > 0) {
        quality = fileObj.quality;
      }
      // quality值越小，所绘制出的图像越模糊
      const data = canvas.toDataURL("image/jpeg", quality);
      // 压缩完成执行回调
      const newFile = convertBase64UrlToBlob(data);
      callback(newFile);
    };
  } catch (e) {
    console.log("压缩失败!");
  }
}

function convertBase64UrlToBlob(urlData) {
  const bytes = window.atob(urlData.split(",")[1]); // 去掉url的头，并转换为byte
  // 处理异常,将ascii码小于0的转换为大于0
  const ab = new ArrayBuffer(bytes.length);
  const ia = new Uint8Array(ab);
  for (let i = 0; i < bytes.length; i++) {
    ia[i] = bytes.charCodeAt(i);
  }
  return new Blob([ab], { type: "image/png" });
}