解决IE10以下浏览器不能编码Base64字符的问题

一、问题描述

　　前几天发现写的js代码中用到的 window.btoa('mingwen'); 在IE10以下浏览器中报错，不支持此语法。

二、解决方法

　　要兼容IE9、IE8、IE7，我们可以专门针对这些浏览器再引入一段ployfill脚本或者一个JS文件即可。

　　也就是HTML中嵌入下面一段代码：

<!--[if IE]>
<script src="./base64-polyfill.js"></script>
<![endif]-->

　　base64-polyfill.js内容：

(function(f) {

  'use strict';

  /* istanbul ignore else */
  if (typeof exports === 'object' && exports != null &&
      typeof exports.nodeType !== 'number') {
    module.exports = f ();
  } else if (typeof define === 'function' && define.amd != null) {
    define ([], f);
  } else {
    var base64 = f ();
    var global = typeof self !== 'undefined' ? self : $.global;
    if (typeof global.btoa !== 'function') global.btoa = base64.btoa;
    if (typeof global.atob !== 'function') global.atob = base64.atob;
  }

} (function() {

  'use strict';

  var chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';

  function InvalidCharacterError(message) {
    this.message = message;
  }
  InvalidCharacterError.prototype = new Error ();
  InvalidCharacterError.prototype.name = 'InvalidCharacterError';

  // encoder
  // [https://gist.github.com/999166] by [https://github.com/nignag]
  function btoa(input) {
    var str = String (input);
    for (
      // initialize result and counter
      var block, charCode, idx = 0, map = chars, output = '';
      // if the next str index does not exist:
      //   change the mapping table to "="
      //   check if d has no fractional digits
      str.charAt (idx | 0) || (map = '=', idx % 1);
      // "8 - idx % 1 * 8" generates the sequence 2, 4, 6, 8
      output += map.charAt (63 & block >> 8 - idx % 1 * 8)
    ) {
      charCode = str.charCodeAt (idx += 3 / 4);
      if (charCode > 0xFF) {
        throw new InvalidCharacterError ("'btoa' failed: The string to be encoded contains characters outside of the Latin1 range.");
      }
      block = block << 8 | charCode;
    }
    return output;
  }

  // decoder
  // [https://gist.github.com/1020396] by [https://github.com/atk]
  function atob(input) {
    var str = (String (input)).replace (/[=]+$/, ''); // #31: ExtendScript bad parse of /=
    if (str.length % 4 === 1) {
      throw new InvalidCharacterError ("'atob' failed: The string to be decoded is not correctly encoded.");
    }
    for (
      // initialize result and counters
      var bc = 0, bs, buffer, idx = 0, output = '';
      // get next character
      buffer = str.charAt (idx++); // eslint-disable-line no-cond-assign
      // character found in table? initialize bit storage and add its ascii value;
      ~buffer && (bs = bc % 4 ? bs * 64 + buffer : buffer,
        // and if not first of each 4 characters,
        // convert the first 8 bits to one ascii character
        bc++ % 4) ? output += String.fromCharCode (255 & bs >> (-2 * bc & 6)) : 0
    ) {
      // try to find character in table (0-63, not found => -1)
      buffer = chars.indexOf (buffer);
    }
    return output;
  }

  return {btoa: btoa, atob: atob};

}));

　　

三、总结

　　从IE10+浏览器开始，所有浏览器就原生提供了Base64编码解码方法，不仅可以用于浏览器环境，Service Worker环境也可以使用。

　　方法名就是atob和btoa，

　　1、Base64编码

var encodedData = window.btoa(stringToEncode);

　　2、Base64解码

var decodedData = window.atob(encodedData);

　　但是，如果你的项目还有支持IE10以下浏览器的话，可参照上面的解决方法。

参考：

【这位博主写的文章狠不错，墙裂推荐】

https://www.zhangxinxu.com/wordpress/2018/08/js-base64-atob-btoa-encode-decode/