phpjs/functions/strings/quoted_printable_encode.js

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function quoted_printable_encode(str) {
  //  discuss at: http://phpjs.org/functions/quoted_printable_encode/
  // 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'

  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);
}