全部16進数の数値文字参照にするやつ

entity.js

var entity = function(string) {
  return ('' + string).replace(/(?:[\uD800-\uDBFF][\uDC00-\uDFFF]|[\S\s])/g, function(m0) {
    var c = m0.length === 2 ?
      (((m0.charCodeAt(0) & 0x3ff) << 10) | (m0.charCodeAt(1) & 0x3ff)) + 0x10000 :
      m0.charCodeAt(0);
      
    return '&#x' + c.toString(16) + ';';
  });
};