JS里面增加事件

addEvent( object, eventType, function );
addEvent( document.getElementById('foo'), 'click', doSomething );
addEvent( obj, 'mouseover', function(){ alert('hello!'); } );
使用之前，先把下面的代码复制过来：

function addEvent( obj, type, fn ) {
   if ( obj.attachEvent ) {
     obj['e'+type+fn] = fn;
     obj[type+fn] = function(){obj['e'+type+fn]( window.event );}
     obj.attachEvent( 'on'+type, obj[type+fn] );
   } else
     obj.addEventListener( type, fn, false );
}
function removeEvent( obj, type, fn ) {
   if ( obj.detachEvent ) {
     obj.detachEvent( 'on'+type, obj[type+fn] );
     obj[type+fn] = null;
   } else
     obj.removeEventListener( type, fn, false );
}