Decode HTML entities in a string

htmlDecode.js

/*
 * decode HTML entities in a string
 * usage examples: 
 *   htmlDecode('foo & bar') => 'foo & bar'
 *   htmlDecode('foo/bar')   => 'foo/bar'
 */
let htmlDecode = function(str) {
  const map = {
    '&' :   '&',
    '>'  :   '>',
    '&lt;'  :   '<',
    '&quot;':   '"',
    '&#39;' :   "'"
  };

  // this could easily be optimized so that the regex is only
  // generated on the first call. right now it is re-generated
  // on every function invocation.
  const re = new RegExp('(' + Object.keys(map).join('|') + '|&#[0-9]{1,5};|&#x[0-9a-fA-F]{1,4};' + ')', 'g');
        
  return String(str).replace(re, function(match, capture) {
    return (capture in map) ? map[capture] :
      capture[2] === 'x' ? 
        String.fromCharCode(parseInt(capture.substr(3), 16)) :
        String.fromCharCode(parseInt(capture.substr(2), 10));
  });
};