学步园

document.getElementByClass = function (classname) {
   var elements = [];
   var alltags = document.all ? document.all : document.getElementsByTagName("*")
   for (var i=0; i<alltags.length; i++) {
      var classNames = alltags[i].className.split(" ");
      if (classNames.contain(classname))
          elements[elements.length] = alltags[i];
   }
   return elements;
}