通过clss属性查找元素

function hasClass(name,type) { 
     var r = []; 
     // Locate the class name (allows for multiple class names) 
     var re = new RegExp("(^|\\s)" + name + "(\\s|$)"); 
     // Limit search by type, or look through all elements 
              var e = document.getElementsByTagName(type || "*"); 
              for ( var j = 0; j < e.length; j++ ) 
                   // If the element has the class, add it for return 
                   if ( re.test(e[j]) ) r.push( e[j] ); 

              // Return the list of matched elements 
              return r; 
}