document.onreadystatechange = subSomething;//当页面加载状态改变的时候执行这个方法. 
function subSomething() 
{ 
if(document.readyState == “complete”) //当页面加载完成后
//执行语句
}

页面加载readyState的五种状态 
0: (Uninitialized) the send( ) method has not yet been invoked. 
1: (Loading) the send( ) method has been invoked, request in progress. 
2: (Loaded) the send( ) method has completed, entire response received. 
3: (Interactive) the response is being parsed. 
4: (Completed) the response has been parsed, is ready for harvesting. 

翻译成中文为: 
0 － （未初始化）还没有调用send()方法 
1 － （载入）已调用send()方法，正在发送请求 
2 － （载入完成）send()方法执行完成，已经接收到全部响应内容 
3 － （交互）正在解析响应内容 
4 － （完成）响应内容解析完成，可以在客户端调用了