下午遇到一个业务场景，导出excel数据的接口。http 200 的时候判断返回值，前端提示有没有导出功能。因为是下载文件，所以我设置的 responseTy="arraybuffer"。这时候就出问题了，如果后端给我的不是文件，是异常信息，我识别不了。所以就需要有 ArrayBuffer 转换成 String 的需求

涉及到的环境

• axios
• ArrayBuffer

在网上查找了下， 发现大部分的都是对 ArrayBuffer 的说明，没有涉及到转换的事情

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最终代码

/**
 * 将 ArrayBuffer 转换成 String
 * @param {*} arrayBuffer 
 */
const decodeUtf8 = (arrayBuffer) => {
  var result = "";
  var i = 0;
  var c = 0;
  var c1 = 0;
  var c2 = 0;
  var c3 = 0; 

  var data = new Uint8Array(arrayBuffer);

  // If we have a BOM skip it
  if (data.length >= 3 && data[0] === 0xef && data[1] === 0xbb && data[2] === 0xbf) {
    i = 3;
  }

  while (i < data.length) {
    c = data[i];

    if (c < 128) {
      result += String.fromCharCode(c);
      i++;
    } else if (c > 191 && c < 224) {
      if (i + 1 >= data.length) {
        throw "UTF-8 Decode failed. Two byte character was truncated.";
      }
      c2 = data[i + 1];
      result += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
      i += 2;
    } else {
      if (i + 2 >= data.length) {
        throw "UTF-8 Decode failed. Multi byte character was truncated.";
      }
      c2 = data[i + 1];
      c3 = data[i + 2];
      result += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
      i += 3;
    }
  }
  return result;
}

/**
 * 导出文件
 * @param {Object} 
 *      data:Object 参数
 *      url: String 地址
 *      method: String 
 *      fileName: String 文件名称
 */
function DownloadFileBinary({ data, url, method = "POST", fileName = '下载文件' }) {
    axios({
      method,
      url,
      data,
      responseType: "arraybuffer"
    })
      .then(res => {
        // 将arraybuffer to json
        let str = decodeUtf8(res);
        let json = JSON.parse(str);
        if (!json.state) {
          Message({
            type: "error",
            message: json.message
          });
          return false;
        }
        console.log(res, "-----------------");
        let blob = new Blob([res], {
          type: "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
        });
        if (window.navigator.msSaveBlob) {
          // for ie 10 and later
          try {
            let url = fileName;
            console.log(url); // IE 需要引用一下才能获取变量的值
            window.navigator.msSaveBlob(blob, url);
          } catch (e) {
            console.error(e);
          }
        } else {
          // let objecturl = URL.createObjectURL(blob);
          // window.location.href = objecturl;

          let link = document.createElement("a");
          document.querySelector("body").appendChild(link);
          link.href = window.URL.createObjectURL(blob);
          link.download = fileName;
          link.click();
          window.URL.revokeObjectURL(link.href);
          document.querySelector("body").removeChild(link);
        }
      })
      .catch(err => {

      });
  },