getElementsByClassName.js

  function getElementsByClassName(clsName, element) {
      var arr = [];

      var aEle = element.getElementsByTagName('*');

      var re = new RegExp('\\b'+ clsName +'\\b');

      for (var i= 0,len=aEle.length; i<len; i++) {
          if (re.test(aEle[i].className)) {
              arr.push(aEle[i]);
          }
      }

      return arr;
  }