[Old Pedant]

This is crazy:

function validInt(value)
{
    for (var i=0; i < value.length; i++) {
        var c = value.charAt(i);
        if ((c < '0' || c > '9') && c != '.') {
            alert("There's a problem: all values herein must " +
                    "be numbers only, and " + value + 
                    " has an unacceptable character " + "'" + c + "'");
            return(false);
       }
    }
    return(true);
}

validInt??? Integers do *NOT* have decimal points, so what in the world is the test for period doing in there?

On top of that, as written that code would *ALLOW* input such as ".........." or "3........9" or "3.999999999999", none of which make a lot of sense.

If you want to check for a valid number--and here I will assume it is to be no more than 2 digits after the decimal point (i.e., dollars and cents) then:

function validNum( value )
{
    if ( ( /^\-?(\.\d\d?|\d+(\.\d?\d?)?)$/ ).test( value ) { return true; }
    document.getElementById("errorMessage") = 
          "That is not a valid dollars and cents value";
    return false;
}

The \-? in red is optional, if you want to allow negative numbers.

Notice that this also avoids the use of alert( ), which is obsolete.

But if you aren't so fussy--if you *WILL* allow numbers such as 3.9999999 or 13E2--then let JS test for you:

if ( isNaN( value ) ) { ... not a valid number ... } else { ... valid ... }