Application Express :: Passing Variable To Javascript

4.1.2theme 24

I have a .js process in the before header of a page which has this pl/sql process using htp script javascript function {code} 

function check(flag_val){ if(flag_val=="N") 
document.getElementById("btn").disabled = true;
else 
document.getElementById("btn").disabled = false;  } 
{code} 

and then there is the actual pl/sql process which  has a cursor 

{code} 
declareflg varchar2(1);
..begin selectflag into v_flagfrom table where rownum = 1;
-- actual conditions are different but this returns one value.

 Then below using htp package I had html table with something like 

<td align="right">
<button class="btn btn-success" type="button" id="btn"  onclick="check(flg);"
title="Accept Lead" style=" width:50px;">Flag value</button> </td>  
 {code}

For some reason the script function is not called if I use onload. If I change the onload to onclick it works. Also, if I pass check(flg) it does not work. If I use check(''N'') then is works fine. question is how do I pass a pl/sql variable flg in this case to a javascript function as a parameter? I basically, want the value of flg checked on page load and then if it is N then disable the button. Or else keep it enabled.