save as (front end file saver)

saveAs.js

;(function(self) {
  'use strict';
  /**
   * 将base64数据转成Blob对象，
   * @param  {string} base64 base64字符串
   * @param  {string} type   mime type
   * @param  {number} size   slice size
   * @return {object}        Blob对象
   */
  function b2b(base64) {
    var decode, i, length, byteArray;
    i = 0;
    decode = atob(base64);
    length = decode.length;
    byteArray = new Uint8Array(length);

    for (;i < length;i++) {
      byteArray[i] = decode.charCodeAt(i);
    }
    return new Blob([byteArray]);
  }

  /**
   * 将base64数据解码并保存文件
   * @param  {string} base64   base64字符
   * @param  {string} filename 文件名
   * @return {undefined}       
   */
  function saveAs(base64, filename) {
    var a, blob, url;
    a = self.document.createElementNS('http://www.w3.org/1999/xhtml', 'a');
    blob = b2b(base64);
    url = self.URL.createObjectURL(blob);
    a.href = url;
    a.download = filename;
    a.click();
    self.URL.revokeObjectURL(url);
  }
  self.saveAs = saveAs;
})(self || window || this.content);