ASP.NET Gridview and checkbox all but none of the implementation code

1. Page "transmits itself" in onclick event

 
<asp:TemplateField HeaderText=" Future generations "> 
<HeaderTemplate> 
<input type="checkbox" id="CheckBox1" name="CheckBox1" onclick="GetAllCheckBox(this)" /> 
 Future generations  
</HeaderTemplate> 
<ItemTemplate> 
<asp:CheckBox ID="CheckBox2" runat="server"/> 
</ItemTemplate> 
<ItemStyle HorizontalAlign="Center" Width="100px" /> 
</asp:TemplateField> 

2. Write JS code

 
<script type="text/javascript" language="javascript"> 
function GetAllCheckBox(CheckAll) 
{ 
var items = document.getElementsByTagName("input"); 
for(var i=0;i<items.length;i++) 
{ 
if(items[i].type == "checkbox") 
{ 
items[i].checked = CheckAll.checked; 
} 
} 
} 
</script>