Question

I want to see whether an item in my array was created today, so I’m using an arrayFilter to filter each element in my array, the problem is, I can’t get my filter to work properly:

return ko.utils.arrayFilter(self.enquiries(), function (enquiry) {
    var include = true;

    if (self.onlyToday()) {
        var formatted = $.datepicker.formatDate("dd/mm/yy", new Date());

        include = include && +enquiry.EnquiryDate.indexOf(+formatted > -1);
    }

    return include;
});

Here is what my data looks like:

formatted: 26/11/2012
enquiry.EnquiryDate: 08/11/2012 08:46:46 

So obviously, this enquiry should be filtered as it wasn’t created today.

Answer 1

There are several problems here.

1. You’re putting a string in formatted, then later using +formatted > -1. +formatted will always be NaN, which is never > -1 (it’s also never equal to -1 and never < -1).

2. You’re setting include to true and then doing include = include && .... The part following the && will never be evaluated, because the part to the left of && is true and JavaScript (like most modern languages) short-circuits expressions.

3. If enquiry refers to an object, +enquiry will probably be NaN unless you’ve overridden its valueOf.

4. You’re comparing strings, which means the most significant parts of the comparison will be on the left — but your date strings are in a format where the most significant values are on the right. So for example, the string "01/01/2013" is less than the string "02/02/2012", even though of course that’s not true of the dates they represent. If you want to meaningfully compare date strings, they must have the year on the left, followed by the month, followed by the day.

Based on your quoted enquiry.EnquiryDate string, you can do this:

var today = $.datepicker.formatDate("yy/mm/dd", new Date());
return ko.utils.arrayFilter(self.enquiries(), function (enquiry) {
    var parts, enqDate;

    parts = enquiry.EnquiryDate.split(' ')[0].split('/');
    enqDate = parts[2] + '/' + parts[1] + '/' + parts[0];
    return enqDate === today;
});

Notes on the above:

• Note that I’m getting today’s date with the year on the left.

• I’ve removed the self.onlyToday() bit because the filter didn’t do anything if self.onlyToday() was false. My guess is you want that check outside this filter function, and you’re either going to call this filter, or not.

• Since enquiry.EnquiryDate is a date and time string, separated with a space, first we split it on a space, then we take the first part (the date) and split it on the /. Then we recombine that in yy/mm/dd order.

• Now we know we can do the === on the strings to see if the enquiry date equals today.

You could, of course, do this comparison using Date objects, but as you’d just have to parse the enquiry.EnquiryDate strings into Date objects anyway, and you only want day resolution (not millisecond resolution), using a string compare seems reasonable.