JS模拟a链接下载文件流

/**
 * 模拟a链接下载导出方法
 * @param {blob} data 数据源
 * @param {string} strFileName下载导出文件名 默认 'download'
 * @param {string} strFileType 文件类型 默认 'xlsx'
 */

export function downloadFn(data, strFileName, strFileType) {

  var self = window,
    defaultType = "application/octet-stream",
    docType = strFileType || defaultType,
    payload = data,
    //避免带中文的文件名赋值给url
    //url = !strFileName && !strFileType && payload,
    url = payload,
    anchor = document.createElement("a"),
    toString = function(a) {
      return String(a);
    },
    myBlob = (self.Blob || self.MozBlob || self.WebKitBlob || toString),
    fileName = strFileName || "download",
    blob,
    reader;
  myBlob = myBlob.call ? myBlob.bind(self) : Blob;

  if (String(this) === "true") {
    payload = [payload, docType];
    docType = payload[0];
    payload = payload[1];
  }


  if (url && url.length < 2048) {
    if (strFileName) {
      fileName = strFileName;
    } else {
      fileName = url.split("/").pop().split("?")[0];
    }
    anchor.href = url;
    //带中文url
    //   if(anchor.href.indexOf(url) !== -1){
    var ajax = new XMLHttpRequest();
    ajax.open("GET", url, true);
    ajax.responseType = 'blob';
    ajax.onload = function(e) {
      download(e.target.response, fileName, defaultType);
    };
    setTimeout(function() {
      ajax.send();
    }, 0);
    return ajax;
    // }
  }


  if (/^data\:[\w+\-]+\/[\w+\-]+[,;]/.test(payload)) {

    if (payload.length > (1024 * 1024 * 1.999) && myBlob !== toString) {
      payload = dataUrlToBlob(payload);
      docType = payload.type || defaultType;
    } else {
      return navigator.msSaveBlob ?
        navigator.msSaveBlob(dataUrlToBlob(payload), fileName) :
        saver(payload);
    }

  }

  blob = payload instanceof myBlob ?
    payload :
    new myBlob([payload], {
      type: docType
    });


  function dataUrlToBlob(strUrl) {
    var parts = strUrl.split(/[:;,]/),
      type = parts[1],
      decoder = parts[2] == "base64" ? atob : decodeURIComponent,
      binData = decoder(parts.pop()),
      mx = binData.length,
      i = 0,
      uiArr = new Uint8Array(mx);

    for (i; i < mx; ++i) uiArr[i] = binData.charCodeAt(i);

    return new myBlob([uiArr], {
      type: type
    });
  }

  function saver(url, winMode) {

    if ('download' in anchor) {
      anchor.href = url;
      anchor.setAttribute("download", fileName);
      anchor.className = "download-js-link";
      anchor.innerHTML = "downloading...";
      anchor.style.display = "none";
      document.body.appendChild(anchor);
      setTimeout(function() {
        anchor.click();
        document.body.removeChild(anchor);
        if (winMode === true) {
          setTimeout(function() {
            self.URL.revokeObjectURL(anchor.href);
          }, 250);
        }
      }, 66);
      return true;
    }


    if (/(Version)\/(\d+)\.(\d+)(?:\.(\d+))?.*Safari\//.test(navigator.userAgent)) {
      url = url.replace(/^data:([\w\/\-\+]+)/, defaultType);
      if (!window.open(url)) {
        if (window.confirm(
            "Displaying New Document\n\nUse Save As... to download, then click back to return to this page.")) {
          window.location.href = url;
        }
      }
      return true;
    }


    var f = document.createElement("iframe");
    document.body.appendChild(f);

    if (!winMode) {
      url = "data:" + url.replace(/^data:([\w\/\-\+]+)/, defaultType);
    }
    f.src = url;
    setTimeout(function() {
      document.body.removeChild(f);
    }, 333);

  }




  if (navigator.msSaveBlob) {
    return navigator.msSaveBlob(blob, fileName);
  }

  if (self.URL) {
    saver(self.URL.createObjectURL(blob), true);
  } else {

    if (typeof blob === "string" || blob.constructor === toString) {
      try {
        return saver("data:" + docType + ";base64," + self.btoa(blob));
      } catch (y) {
        return saver("data:" + docType + "," + encodeURIComponent(blob));
      }
    }


    reader = new FileReader();
    reader.onload = function(e) {
      saver(this.result);
    };
    reader.readAsDataURL(blob);
  }
  return true;
};