var timer; 
function showMessage(){ 
var obj=document.getElementById("mydiv"); 
obj.style.display="block"; 
}
function begin(){//调用此函数，显示正在加载提示 
timer=setInterval(showMessage,0); 
}
function end(){//调用此函数，关闭加载提示 
clearInterval(timer); 
hideMessage(); 
}
function hideMessage(){ 
document.getElementById("mydiv").style.display="none"; 
}