javascript 鼠标点击事件

//javascript点击页面，判断鼠标左键，右键，中键点击事件

<script language=javascript>
  function click()
   {
       if (event.button == 1)
       {
           alert('left');
       }
       if (event.button == 2)
       {
            alert('right');                
       }
       if(event.button == 4)
       {
           alert('middle');
       }
    }
   document.onmousedown = click;
</script>