母板页子页下的服务器控件ID问题

Question

<%@ Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Default4.aspx.cs" Inherits="Default4" Title="Untitled Page" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<div>
<asp:TextBox ID="TextBox1" runat="server" onblur="show()"></asp:TextBox><br />
        <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox></div>
</asp:Content>我如何用js取得Textbox1?
这样得到document.getElementById('TextBox1')得不到！
因为运行后
<div>
<input name="ctl00$ContentPlaceHolder1$TextBox1" type="text" id="ctl00_ContentPlaceHolder1_TextBox1" onblur="show()" /><br />
        <input name="ctl00$ContentPlaceHolder1$TextBox2" type="text" id="ctl00_ContentPlaceHolder1_TextBox2" />&nbsp;<input id="Text1" type="text" /></div>
请问用js如何才能取得TextBox1呢？急.....

Answer 1

var txtObj = document.getElementById('<%=TextBox1.ClientID %>');

Answer 2

document.getElementById('MasterPage_TextBox1')

Answer 3

document.getElementById("<%=TextBox1.ClientID %>");

Answer 4

document.getElementById('<%=TextBox1.ClientID %>');这个就行