function quoted_printable_encode (str) {
  // +   original by: Theriault
  // +   improved by: Brett Zamir (http://brett-zamir.me)
  // +   improved by: Theriault
  // *     example 1: quoted_printable_encode('a=b=c');
  // *     returns 1: 'a=3Db=3Dc'
  // *     example 2: quoted_printable_encode('abc   \r\n123   \r\n');
  // *     returns 2: 'abc  =20\r\n123  =20\r\n'
  // *     example 3: quoted_printable_encode('0123456789012345678901234567890123456789012345678901234567890123456789012345');
  // *     returns 3: '012345678901234567890123456789012345678901234567890123456789012345678901234=\r\n5'
  // RFC 2045: 6.7.2: Octets with decimal values of 33 through 60 (bang to less-than) inclusive, and 62 through 126 (greater-than to tilde), inclusive, MAY be represented as the US-ASCII characters
  // PHP does not encode any of the above; as does this function.
  // RFC 2045: 6.7.3: Octets with values of 9 and 32 MAY be represented as US-ASCII TAB (HT) and SPACE characters, respectively, but MUST NOT be so represented at the end of an encoded line
  // PHP does not encode spaces (octet 32) except before a CRLF sequence as stated above. PHP always encodes tabs (octet 9). This function replicates PHP.
  // RFC 2045: 6.7.4: A line break in a text body, represented as a CRLF sequence in the text canonical form, must be represented by a (RFC 822) line break
  // PHP does not encode a CRLF sequence, as does this function.
  // RFC 2045: 6.7.5: The Quoted-Printable encoding REQUIRES that encoded lines be no more than 76 characters long. If longer lines are to be encoded with the Quoted-Printable encoding, "soft" line breaks must be used.
  // PHP breaks lines greater than 76 characters; as does this function.
  var hexChars = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'],
    RFC2045Encode1IN = / \r\n|\r\n|[^!-<>-~ ]/gm,
    RFC2045Encode1OUT = function (sMatch) {
      // Encode space before CRLF sequence to prevent spaces from being stripped
      // Keep hard line breaks intact; CRLF sequences
      if (sMatch.length > 1) {
        return sMatch.replace(' ', '=20');
      }
      // Encode matching character
      var chr = sMatch.charCodeAt(0);
      return '=' + hexChars[((chr >>> 4) & 15)] + hexChars[(chr & 15)];
    },
    // Split lines to 75 characters; the reason it's 75 and not 76 is because softline breaks are preceeded by an equal sign; which would be the 76th character.
    // However, if the last line/string was exactly 76 characters, then a softline would not be needed. PHP currently softbreaks anyway; so this function replicates PHP.
    RFC2045Encode2IN = /.{1,72}(?!\r\n)[^=]{0,3}/g,
    RFC2045Encode2OUT = function (sMatch) {
      if (sMatch.substr(sMatch.length - 2) === '\r\n') {
        return sMatch;
      }
      return sMatch + '=\r\n';
    };
  str = str.replace(RFC2045Encode1IN, RFC2045Encode1OUT).replace(RFC2045Encode2IN, RFC2045Encode2OUT);
  // Strip last softline break
  return str.substr(0, str.length - 3);
}

quoted_printable_encode('a=b=c');

'a=3Db=3Dc'

quoted_printable_encode('abc   \r\n123   \r\n');

'abc  =20\r\n123  =20\r\n'

quoted_printable_encode('0123456789012345678901234567890123456789012345678901234567890123456789012345');

'012345678901234567890123456789012345678901234567890123456789012345678901234=\r\n5'