Есть ли какая-то функция, которую я могу использовать в PHP или javascript для преобразования ВСЕХ HTML-объектов в их десятичные эквиваленты?

<?php
$entities = getEntities();
$from = array();
$to = array();

foreach ($entities as $ent => $code) {
    $from[] = '&' . $ent . ';';
    $to[] = '&#' . $code . ';';
}

$str = '&xi; and &tau;';

// you can pass arrays to str_replace
// see http://php.net/manual/en/function.str-replace.php
echo str_replace($from, $to, $str);

function getEntities() {
    // http://www.mit.edu/afs.new/sipb/project/php/include/entities.h
    return array(
        'AElig'    => 198,
        'Aacute'   => 193,
        'Acirc'    => 194,
        'Agrave'   => 192,
        'Alpha'    => 913,
        'Aring'    => 197,
        'Atilde'   => 195,
        'Auml'     => 196,
        'Beta'     => 914,
        'Ccedil'   => 199,
        'Chi'      => 935,
        'Dagger'   => 8225,
        'Delta'    => 916,
        'ETH'      => 208,
        'Eacute'   => 201,
        'Ecirc'    => 202,
        'Egrave'   => 200,
        'Epsilon'  => 917,
        'Eta'      => 919,
        'Euml'     => 203,
        'Gamma'    => 915,
        'Iacute'   => 205,
        'Icirc'    => 206,
        'Igrave'   => 204,
        'Iota'     => 921,
        'Iuml'     => 207,
        'Kappa'    => 922,
        'Lambda'   => 923,
        'Mu'       => 924,
        'Ntilde'   => 209,
        'Nu'       => 925,
        'OElig'    => 338,
        'Oacute'   => 211,
        'Ocirc'    => 212,
        'Ograve'   => 210,
        'Omega'    => 937,
        'Omicron'  => 927,
        'Oslash'   => 216,
        'Otilde'   => 213,
        'Ouml'     => 214,
        'Phi'      => 934,
        'Pi'       => 928,
        'Prime'    => 8243,
        'Psi'      => 936,
        'Rho'      => 929,
        'Scaron'   => 352,
        'Sigma'    => 931,
        'THORN'    => 222,
        'Tau'      => 932,
        'Theta'    => 920,
        'Uacute'   => 218,
        'Ucirc'    => 219,
        'Ugrave'   => 217,
        'Upsilon'  => 933,
        'Uuml'     => 220,
        'Xi'       => 926,
        'Yacute'   => 221,
        'Yuml'     => 376,
        'Zeta'     => 918,
        'aacute'   => 225,
        'acirc'    => 226,
        'acute'    => 180,
        'aelig'    => 230,
        'agrave'   => 224,
        'alefsym'  => 8501,
        'alpha'    => 945,
        'amp'      => 38,
        'and'      => 8743,
        'ang'      => 8736,
        'aring'    => 229,
        'asymp'    => 8776,
        'atilde'   => 227,
        'auml'     => 228,
        'bdquo'    => 8222,
        'beta'     => 946,
        'brvbar'   => 166,
        'bull'     => 8226,
        'cap'      => 8745,
        'ccedil'   => 231,
        'cedil'    => 184,
        'cent'     => 162,
        'chi'      => 967,
        'circ'     => 710,
        'clubs'    => 9827,
        'cong'     => 8773,
        'copy'     => 169,
        'crarr'    => 8629,
        'cup'      => 8746,
        'curren'   => 164,
        'dArr'     => 8659,
        'dagger'   => 8224,
        'darr'     => 8595,
        'deg'      => 176,
        'delta'    => 948,
        'diams'    => 9830,
        'divide'   => 247,
        'eacute'   => 233,
        'ecirc'    => 234,
        'egrave'   => 232,
        'empty'    => 8709,
        'emsp'     => 8195,
        'ensp'     => 8194,
        'epsilon'  => 949,
        'equiv'    => 8801,
        'eta'      => 951,
        'eth'      => 240,
        'euml'     => 235,
        'euro'     => 8364,
        'exist'    => 8707,
        'fnof'     => 402,
        'forall'   => 8704,
        'frac12'   => 189,
        'frac14'   => 188,
        'frac34'   => 190,
        'frasl'    => 8260,
        'gamma'    => 947,
        'ge'       => 8805,
        'gt'       => 62,
        'hArr'     => 8660,
        'harr'     => 8596,
        'hearts'   => 9829,
        'hellip'   => 8230,
        'iacute'   => 237,
        'icirc'    => 238,
        'iexcl'    => 161,
        'igrave'   => 236,
        'image'    => 8465,
        'infin'    => 8734,
        'int'      => 8747,
        'iota'     => 953,
        'iquest'   => 191,
        'isin'     => 8712,
        'iuml'     => 239,
        'kappa'    => 954,
        'lArr'     => 8656,
        'lambda'   => 955,
        'lang'     => 9001,
        'laquo'    => 171,
        'larr'     => 8592,
        'lceil'    => 8968,
        'ldquo'    => 8220,
        'le'       => 8804,
        'lfloor'   => 8970,
        'lowast'   => 8727,
        'loz'      => 9674,
        'lrm'      => 8206,
        'lsaquo'   => 8249,
        'lsquo'    => 8216,
        'lt'       => 60,
        'macr'     => 175,
        'mdash'    => 8212,
        'micro'    => 181,
        'middot'   => 183,
        'minus'    => 8722,
        'mu'       => 956,
        'nabla'    => 8711,
        'nbsp'     => 160,
        'ndash'    => 8211,
        'ne'       => 8800,
        'ni'       => 8715,
        'not'      => 172,
        'notin'    => 8713,
        'nsub'     => 8836,
        'ntilde'   => 241,
        'nu'       => 957,
        'oacute'   => 243,
        'ocirc'    => 244,
        'oelig'    => 339,
        'ograve'   => 242,
        'oline'    => 8254,
        'omega'    => 969,
        'omicron'  => 959,
        'oplus'    => 8853,
        'or'       => 8744,
        'ordf'     => 170,
        'ordm'     => 186,
        'oslash'   => 248,
        'otilde'   => 245,
        'otimes'   => 8855,
        'ouml'     => 246,
        'para'     => 182,
        'part'     => 8706,
        'permil'   => 8240,
        'perp'     => 8869,
        'phi'      => 966,
        'pi'       => 960,
        'piv'      => 982,
        'plusmn'   => 177,
        'pound'    => 163,
        'prime'    => 8242,
        'prod'     => 8719,
        'prop'     => 8733,
        'psi'      => 968,
        'quot'     => 34,
        'rArr'     => 8658,
        'radic'    => 8730,
        'rang'     => 9002,
        'raquo'    => 187,
        'rarr'     => 8594,
        'rceil'    => 8969,
        'rdquo'    => 8221,
        'real'     => 8476,
        'reg'      => 174,
        'rfloor'   => 8971,
        'rho'      => 961,
        'rlm'      => 8207,
        'rsaquo'   => 8250,
        'rsquo'    => 8217,
        'sbquo'    => 8218,
        'scaron'   => 353,
        'sdot'     => 8901,
        'sect'     => 167,
        'shy'      => 173,
        'sigma'    => 963,
        'sigmaf'   => 962,
        'sim'      => 8764,
        'spades'   => 9824,
        'sub'      => 8834,
        'sube'     => 8838,
        'sum'      => 8721,
        'sup'      => 8835,
        'sup1'     => 185,
        'sup2'     => 178,
        'sup3'     => 179,
        'supe'     => 8839,
        'szlig'    => 223,
        'tau'      => 964,
        'there4'   => 8756,
        'theta'    => 952,
        'thetasym' => 977,
        'thinsp'   => 8201,
        'thorn'    => 254,
        'tilde'    => 732,
        'times'    => 215,
        'trade'    => 8482,
        'uArr'     => 8657,
        'uacute'   => 250,
        'uarr'     => 8593,
        'ucirc'    => 251,
        'ugrave'   => 249,
        'uml'      => 168,
        'upsih'    => 978,
        'upsilon'  => 965,
        'uuml'     => 252,
        'weierp'   => 8472,
        'xi'       => 958,
        'yacute'   => 253,
        'yen'      => 165,
        'yuml'     => 255,
        'zeta'     => 950,
        'zwj'      => 8205,
        'zwnj'     => 8204,
    );
}

?>