hiding isNan message

lloyd_m · February 28th, 2005, 06:19 AM

I have created a restaurant booking system using JavaScript/ASP. The problem I have is in the booking page where I have written IF statements to check that both the txtcustID and txtSeatNo boxes are completed, and then a further ELSE IF statement makes sure that the customer has not tried to book more seats than is available.

This works fine, except I am getting the default isNaN pop up box before my ALERT message kicks in. For example, if the customer leaves the CustID text box blank, then the isNan pops up, clicking OK then brings up the message telling the customer to complete this field.

My question is this. Is it possible to hide the isNan message and go straight to my ALERT?

Here is the code: -

<SCRIPT LANGUAGE=JavaScript>
    function form1_onsubmit()
    {
        var form = document.form1;
        var returnValue = false;
        var seatspassed = (form.txtSeatsLeft.value);
        var seatswanted = (form.txtSeatNo.value);
        var possible = parseInt(seatspassed) - parseInt(seatswanted);

        alert (possible);

        if (form.txtCustID.value == "")
        {
        alert ("Please enter your Customer ID");
        form.txtCustID.focus();
        }
        else if (form.txtSeatNo.value == "")
        {
        alert ("Please enter the number of seats you would like to book");
        form.txtSeatNo.focus();
        }
        else if (possible < 0)
        {
        alert ("There are only " + seatspassed + " seats available. Please try again.");
        form.txtSeatNo.focus();
        }
        else
        {
        returnValue = true;
        }
        return returnValue;
    }
    </SCRIPT>

joefawcett · February 28th, 2005, 06:41 AM

You need to test for NaN before you attempt any arithmetic.
I would never use parseInt, especially without the second argument (which base to covert to), for converting numbers like this, use Math.floor. Try this

Code:

alert(parseInt("012");
alert(parseInt("012", 10);
alert(parseInt("012", 8);
alert(Math.floor("012");

So:

Code:

var seatspassed = (form.txtSeatsLeft.value);
var iSeatsPassed = Math.floor(seatspassed);
if (isNaN(iSeatsPassed))
{
  //alert and exit
}
//repeat for seatswanted

--

Joe (Microsoft MVP - XML)

lloyd_m · February 28th, 2005, 08:38 AM

Thanks Joe,

Funny thing though; The programme works perfectly now I have powered off then on again - probably something to do with running this through IIS. Getting rid of the 'alert(possible)' also helped (I put this in just to check that the variable contained a value).

Still, you're right about testing for NaN before running the IF statement and I'll try your suggestion.

Thanks again.