phpjs/functions/strings/quoted_printable_decode.js

php.js offers community built php functions in javascript

function quoted_printable_decode(str) {
  //       discuss at: http://phpjs.org/functions/quoted_printable_decode/
  //      original by: Ole Vrijenhoek
  //      bugfixed by: Brett Zamir (http://brett-zamir.me)
  //      bugfixed by: Theriault
  // reimplemented by: Theriault
  //      improved by: Brett Zamir (http://brett-zamir.me)
  //        example 1: quoted_printable_decode('a=3Db=3Dc');
  //        returns 1: 'a=b=c'
  //        example 2: quoted_printable_decode('abc  =20\r\n123  =20\r\n');
  //        returns 2: 'abc   \r\n123   \r\n'
  //        example 3: quoted_printable_decode('012345678901234567890123456789012345678901234567890123456789012345678901234=\r\n56789');
  //        returns 3: '01234567890123456789012345678901234567890123456789012345678901234567890123456789'
  //        example 4: quoted_printable_decode("Lorem ipsum dolor sit amet=23, consectetur adipisicing elit");
  //        returns 4: 'Lorem ipsum dolor sit amet#, consectetur adipisicing elit'

  var RFC2045Decode1 = /=\r\n/gm,
    // Decodes all equal signs followed by two hex digits
    RFC2045Decode2IN = /=([0-9A-F]{2})/gim,
    // the RFC states against decoding lower case encodings, but following apparent PHP behavior
    // RFC2045Decode2IN = /=([0-9A-F]{2})/gm,
    RFC2045Decode2OUT = function(sMatch, sHex) {
      return String.fromCharCode(parseInt(sHex, 16));
    };
  return str.replace(RFC2045Decode1, '')
    .replace(RFC2045Decode2IN, RFC2045Decode2OUT);
}