vb.net - how to use id of a button in if statement using javascript -

i beginner javascript , trying perform arithmetic functions.

here code below:

script

<script language="javascript" type="text/javascript">    function func(a,b)       {         var = document.getelementbyid("a");         var b = document.getelementbyid("b");         if (document.getelementbyid("btnadd").text == 'add')            {               var c = + b;               document.getelementbyid("rslt").innerhtml =c;                      }          } </script> 

aspx

<asp:button id="btnadd" text="add" runat="server" onclientclick="func(txtn1,txtn2)" /> <p id="rslt"></p> 

my idea is, when click 'add' button value of 2 textbox should passed script , assigned 2 variables.

with 2 variables arithmetic (add,sub,div,mul) should done.

what pass button clicked, using this. way know text of button clicked. , since using server side button, sure include return false; javascript call prevent posting , clearing <p> tag.

<asp:button id="btnadd" runat="server" text="add"     onclientclick="func('txtn1', 'txtn2', this); return false;" /> 

function func(a, b, btn) {     var txtn1 = document.getelementbyid(a);     var txtn2 = document.getelementbyid(b);     var rslt = document.getelementbyid('rslt');     if(btn.value == 'add')         rslt.innerhtml = parseint(txtn1.value) + parseint(txtn2.value); }