registered button id is already exists check

Hello All,

   i have created dynamic linkbutton and event.every time i have assigned different id .now i want check button id already regitered

then process will not further.so how can i check that is already registred or not??? .if any one have any idea then let me know as earlier as possible.please see below code

function GenerateDynamicLinkButton(param_name, param_id) {

var btn = document.createElement("LinkButton");

btn.setAttribute("id","submit_bttn"+ param_id);

btn.style.width = 40 +"px";      

btn.style.borderBottom ='0px solid #5e97c4';

btn.style.fontWeight ="bold";

btn.innerHTML =" "+" "+param_name;

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

 tdLookup.appendChild(btn);

var x = document.getElementById("submit_bttn"+ param_id);

 x.onclick =function ()

{

ButtonClick(param_id,param_name);

returnfalse;

 }

}

Any help will be appriciated.

Thanks in advance.

Khushboo Nayak