https://www.bellevuechapel.org/js/plugins/base64.js?v=5

1/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
2/*  Base64 class: Base 64 encoding / decoding (c) Chris Veness 2002-2011                          */
3/*    note: depends on Utf8 class                                                                 */
4/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
5
6var Base64 = {};  // Base64 namespace
7
8Base64.code = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
9
10/**
11 * Encode string into Base64, as defined by RFC 4648 [http://tools.ietf.org/html/rfc4648]
12 * (instance method extending String object). As per RFC 4648, no newlines are added.
13 *
14 * @param {String} str The string to be encoded as base-64
15 * @param {Boolean} [utf8encode=false] Flag to indicate whether str is Unicode string to be encoded 
16 *   to UTF8 before conversion to base64; otherwise string is assumed to be 8-bit characters
17 * @returns {String} Base64-encoded string
18 */ 
19Base64.encode = function(str, utf8encode) {  // http://tools.ietf.org/html/rfc4648
20  utf8encode =  (typeof utf8encode == 'undefined') ? false : utf8encode;
21  var o1, o2, o3, bits, h1, h2, h3, h4, e=[], pad = '', c, plain, coded;
22  var b64 = Base64.code;
23   
24  plain = utf8encode ? Utf8.encode(str) : str;
25  
26  c = plain.length % 3;  // pad string to length of multiple of 3
27  if (c > 0) { while (c++ < 3) { pad += '='; plain += '\0'; } }
28  // note: doing padding here saves us doing special-case packing for trailing 1 or 2 chars
29   
30  for (c=0; c<plain.length; c+=3) {  // pack three octets into four hexets
31    o1 = plain.charCodeAt(c);
32    o2 = plain.charCodeAt(c+1);
33    o3 = plain.charCodeAt(c+2);
34      
35    bits = o1<<16 | o2<<8 | o3;
36      
37    h1 = bits>>18 & 0x3f;
38    h2 = bits>>12 & 0x3f;
39    h3 = bits>>6 & 0x3f;
40    h4 = bits & 0x3f;
41
42    // use hextets to index into code string
43    e[c/3] = b64.charAt(h1) + b64.charAt(h2) + b64.charAt(h3) + b64.charAt(h4);
44  }
45  coded = e.join('');  // join() is far faster than repeated string concatenation in IE
46  
47  // replace 'A's from padded nulls with '='s
48  coded = coded.slice(0, coded.length-pad.length) + pad;
49   
50  return coded;
51}
52
53/**
54 * Decode string from Base64, as defined by RFC 4648 [http://tools.ietf.org/html/rfc4648]
55 * (instance method extending String object). As per RFC 4648, newlines are not catered for.
56 *
57 * @param {String} str The string to be decoded from base-64
58 * @param {Boolean} [utf8decode=false] Flag to indicate whether str is Unicode string to be decoded 
59 *   from UTF8 after conversion from base64
60 * @returns {String} decoded string
61 */ 
62Base64.decode = function(str, utf8decode) {
63  utf8decode =  (typeof utf8decode == 'undefined') ? false : utf8decode;
64  var o1, o2, o3, h1, h2, h3, h4, bits, d=[], plain, coded;
65  var b64 = Base64.code;
66
67  coded = utf8decode ? Utf8.decode(str) : str;
68  
69  for (var c=0; c<coded.length; c+=4) {  // unpack four hexets into three octets
70    h1 = b64.indexOf(coded.charAt(c));
71    h2 = b64.indexOf(coded.charAt(c+1));
72    h3 = b64.indexOf(coded.charAt(c+2));
73    h4 = b64.indexOf(coded.charAt(c+3));
74      
75    bits = h1<<18 | h2<<12 | h3<<6 | h4;
76      
77    o1 = bits>>>16 & 0xff;
78    o2 = bits>>>8 & 0xff;
79    o3 = bits & 0xff;
80    
81    d[c/4] = String.fromCharCode(o1, o2, o3);
82    // check for padding
83    if (h4 == 0x40) d[c/4] = String.fromCharCode(o1, o2);
84    if (h3 == 0x40) d[c/4] = String.fromCharCode(o1);
85  }
86  plain = d.join('');  // join() is far faster than repeated string concatenation in IE
87  
88  return utf8decode ? Utf8.decode(plain) : plain; 
89}
90
91/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */