Filtro simple de numeros floats validos

FilterFloat in Javascript.html

<script type="text/javascript">
<!--
function filterFloat(evt){
    // Backspace = 8, Enter = 13, ‘0′ = 48, ‘9′ = 57, ‘.’ = 46, ‘-’ = 43
    var key = window.Event ? evt.which : evt.keyCode;    
    
    if(key >= 48 && key <= 57){
        return true;
    }else{
          if(key == 8 || key == 13 || key == 46) {    
        
              return true;
              
          }else{
              return false;
          }
    }
}

function filter(input){
    var preg = /^([0-9]+\.?[0-9]{0,2})$/; 
    if(preg.test(input.value) === true){
        return true;
    }else{
        if(input.value!= ""){
            alert("Tu numero esta mal solo dos decimales");
            input.focus();
            return false;
        }else{
            return true;
        }
    }
    
}
-->
</script>
<input type="text" name="moneda nac" id="moneda_nac" value="10" onkeyup="return filter(this);" onkeypress="return filterFloat(event);"/>