Check All Checkbox of a grid by using JavaScript

function CheckAllBox()
{
var chkval = document.getElementById('ctl00_cphMain_grdCategory_ctl01_chkAll').checked;
try
{
for(var i=2;i<200;i++)
{
if(i<=9)
{
document.getElementById('ctl00_cphMain_grdCategory_ctl0'+i+'_chk').checked=chkval;
}
else
{
document.getElementById('ctl00_cphMain_grdCategory_ctl'+i+'_chk').checked=chkval;
}
}
}
catch(e){}
}