Converting sanitised html back to displayable html

You could create an element, assign the encoded HTML to its innerHTML and retrieve the nodeValue from the text node created on the insertion.

function htmlDecode(input){
  var e = document.createElement('div');
  e.innerHTML = input;
  return e.childNodes[0].nodeValue;
}

htmlDecode('<div class="someclass"><blockquote> <p>" ' +
           'something" here.</p>Q</blockquote>')

// returns :
// "<div class="someclass"><blockquote> <p>"something" here.</p>Q</blockquote>"

Note that this method should work with all the HTML Character Entities.