JS: Add Event (Vanilla)

gistfile1

var addEvent = (function() {
  return function(elem, type, fn) {
    if (document.addEventListener) {
      if (elem && !elem.length) {
        elem.addEventListener(type, fn, false);
      }
      else if ( elem && elem.length) {
        var len = elem.length;
        for (var i = 0; i < len; i++) {
          addEvent(elem[i], type, fn);
        }
      }
    };
  }
  // is IE
  else if (document.attachEvent) {
    return function (elem, type, fn) {
      if (elem && !elem.length) {
        elem.attachEvent('on' + type, function(){
          return fn.call(elem);
        });
      }
      else if (elem && elem.length) {
        var len = elem.length;
        for (var i = 0; i < len; i++) {
          addEvent(elem[i], type, fn);
        }
      }
    };
  }
})();

// Example:
// var li = document.getElementByTagName('li');
// addEvent(li, 'click', function(e) {
//   this.style.border = '1px solid red';
// });