javascript search json array for date

var startDate = new Date("2015-08-04");
        var endDate = new Date("2015-08-12");

        var resultProductData = product_data.filter(function (a) {
            var hitDates = a.ProductHits || {};
            // extract all date strings
            hitDates = Object.keys(hitDates);
            // improvement: use some. this is an improment because .map()
            // and .filter() are walking through all elements.
            // .some() stops this process if one item is found that returns true in the callback function and returns true for the whole expression
            hitDateMatchExists = hitDates.some(function(dateStr) {
                var date = new Date(dateStr);
                return date >= startDate && date <= endDate
            });
            return hitDateMatchExists;
        });
        console.log(resultProductData);