function numberOnly(num) {
     var vc = "-1234567890."; //strValidCharacters
     var val = "";
     var buf = "";
     for(var i=0;i<num.length;i++) {
          buf = num.substr(i, 1);
          if(vc.indexOf(buf) > -1)
               val += buf;
     }
     x = parseFloat(val);
     return isNaN(x) ? 0 : x;
}

function formatNumber ( elem_name, decimals ) {
    var elem = document.getElementById(elem_name);
    elem.value = numberOnly(elem.value).toFixed(decimals);
}