sheetjs/bits/04_base64.js

var Base64_map = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
function Base64_encode(input) {
  var o = "";
  var c1 = 0, c2 = 0, c3 = 0, e1 = 0, e2 = 0, e3 = 0, e4 = 0;
  for (var i = 0; i < input.length; ) {
    c1 = input.charCodeAt(i++);
    e1 = c1 >> 2;
    c2 = input.charCodeAt(i++);
    e2 = (c1 & 3) << 4 | c2 >> 4;
    c3 = input.charCodeAt(i++);
    e3 = (c2 & 15) << 2 | c3 >> 6;
    e4 = c3 & 63;
    if (isNaN(c2)) {
      e3 = e4 = 64;
    } else if (isNaN(c3)) {
      e4 = 64;
    }
    o += Base64_map.charAt(e1) + Base64_map.charAt(e2) + Base64_map.charAt(e3) + Base64_map.charAt(e4);
  }
  return o;
}
function Base64_decode(input) {
  var o = "";
  var c1 = 0, c2 = 0, c3 = 0, e1 = 0, e2 = 0, e3 = 0, e4 = 0;
  input = input.replace(/[^\w\+\/\=]/g, "");
  for (var i = 0; i < input.length; ) {
    e1 = Base64_map.indexOf(input.charAt(i++));
    e2 = Base64_map.indexOf(input.charAt(i++));
    c1 = e1 << 2 | e2 >> 4;
    o += String.fromCharCode(c1);
    e3 = Base64_map.indexOf(input.charAt(i++));
    c2 = (e2 & 15) << 4 | e3 >> 2;
    if (e3 !== 64) {
      o += String.fromCharCode(c2);
    }
    e4 = Base64_map.indexOf(input.charAt(i++));
    c3 = (e3 & 3) << 6 | e4;
    if (e4 !== 64) {
      o += String.fromCharCode(c3);
    }
  }
  return o;
}