ASP .NET调用javascript中Response.Write和ClientScript.RegisterStartupScript的区别

最近在用ASP .NET的code behind 调用javascript中发现Response.Write不能拿到form的值，而ClientScript.RegisterStartupScript可以。例如下面的代码
1 StringBuilder sb = new StringBuilder();

2 sb.Append("<script language=javascript>");

3 sb.Append("alert(document.forms.length);");

4 sb.Append("</script>");

5

6 Response.Write(sb.ToString());

7 ClientScript.RegisterStartupScript(this.GetType(), "test", sb.ToString());

可以明显的看到，Response.Write得到的是0，ClientScript.RegisterStartupScript得到的是1。