var prev = function(elem){
  do {
    elem = elem.previousSibling;
  } while (elem && elem.nodeType != 1);
  return elem;
}

var next = function(elem){
  do {
    elem = elem.nextSibling;
  } while (elem && elem.nodeType != 1);
  return elem;
}

var hasClass = function(ele,cls) {
	return ele.className.match(new RegExp('(\\s|^)'+cls+'(\\s|$)'));
}
var addClass = function(ele,cls) {
	if (!this.hasClass(ele,cls)) ele.className += " "+cls;
}
var removeClass = function(ele,cls) {
	if (hasClass(ele,cls)) {
		var reg = new RegExp('(\\s|^)'+cls+'(\\s|$)');
		ele.className=ele.className.replace(reg,' ');
	}
}