private void Button2_Click(object sender, System.EventArgs e)
{
System.Web.UI.Control a = Page.FindControl("myplaceholder");
System.Web.UI.HtmlControls.HtmlGenericControl objLink = new HtmlGenericControl("script");
objLink.Attributes.Add("language","javascript");
objLink.Attributes.Add("src","1.js");//这个地方你自己用变量控制
objLink=objLink;
a.Controls.Add(objLink);
}