Javascript to Accept Only Numbers in TextBox

function numbersonly(e, decimal)
{
var key;
var keychar;
if (window.event)
key = window.event.keyCode;
else if (e)
key = e.which;
else
return true;
keychar = String.fromCharCode(key);
if ((key==null) (key==0) (key==8) (key==9) (key==13) (key==27) )
return true;
else if ((("0123456789").indexOf(keychar) > -1))
return true;
else
return false;
}