Repeater and CheckBox problem

Question

Hi friends, I am using a repeater control to bind and list my data from database. I repeater control there will be a checkbox in header temple and a lable. I item template there is checkbox and textbox. Now when ever the header checkbox checked i would like to checked/unchecked all the template items' checkbox. For that i used javascript and add event "onclick" in page load for headercheck box. But now i am not able to get repeater control in my javascript. Here is the code : function WriteToFile() { var ck = document.getElementById('<%=dtrpt.ClientID%>'); var repeater1 = document.getElementById("dtrpt"); alert(ck); alert(repeater1); } IT alert me null. Now what should i do to get repeater in javascsript. And how to checked/unchecked all item checkboxs ? Thanks in advance.