asp.net中如何使一个button先执行后台的Click再执行javascript的onclick?

可以在后台代码里镶嵌JS

前台写好代码 function xxx() {------}

Button事件:
protected void button_Click(object sender, EventArgs e)
{
//
//
//前面写后台代码,后面镶嵌JS
   ClientScript.RegisterStartupScript(Page.GetType(), "", "xxx();", true);
ScriptManager.RegisterStartupScript(gvwJOList, this.GetType(), "magin", "xxx()", true);
   
}