JavaScript loop through Json dates

Question

I'm trying to use JavaScript to loop through a json file which has time periods (starting date/time and ending date/time), and check if now (current date time) falls between any time period in such list.

Following is my code, but can't get where I'm wrong. Any help?

<html>
<script type="text/javascript">
    var data = {
        "period": {
            "startend": [{
                "startDate": "2015-11-17 15:43:37",
                "endDate": "2015-11-18 19:43:37"
            }, {
                "startDate": "2015-12-17 19:43:37",
                "endDate": "2016-01-17 19:43:37"
            }, {
                "startDate": "2015-04-17 19:43:37",
                "endDate": "2015-04-18 19:43:37"
            }]
        }
    }

    var periodArray = data.period.startend;
    var curDate = new Date();
    var datetime = curDate.getFullYear() + '-' + curDate.getMonth() + '-' + curDate.getDate() + ' ' + curDate.getHours() + ':' + curDate.getMinutes() + ':' + curDate.getSeconds();

    for (i = 0; i < periodArray.length ; i++) {
        var obj = periodArray[i]
            if (datetime > obj.startDate && datetime < obj.endDate){
                alert('Falls within period');
            } else {
                alert('Not within any period');
            }
    }
</script>

obj.startDate is just a String. Might want to do new Date(obj.startDate) and so on to get actual dates out of the strings. Then, presumably the comparison between dates will work. — Hunan Rostomyan
– Hunan Rostomyan, Commented Nov 18, 2015 at 0:57
@HunanRostomyan do you mean this: 'if (datetime > new Date(obj.startDate) && datetime < new Date(obj.endDate)){' ? still not working — Harry
– Harry, Commented Nov 18, 2015 at 1:06
Try that piece of code from my response. It has console.log instead of alert, but everything else should be the same. — Hunan Rostomyan
– Hunan Rostomyan, Commented Nov 18, 2015 at 1:16

Hunan Rostomyan · Accepted Answer · 2015-11-18 02:59:13Z

3

The basic idea is to convert the date strings to actual Date objects so they can be compared with the current date (new Date()). Let's begin by defining a helper function that when initialized, closes over the current date, producing a function that takes a start date and an end date, either in String or in Date form, and returns true if and only if the closed over current date is in the range.

Definition.

// () -> (([String|Date] * [String|Date]) -> Boolean)
// When initialized, closes over the current date and returns
// a predicate on String or Date objects. 
function includesNow() {
  var curDate = new Date();
  return function(start, end) {
    var startDate = (typeof start === "string")
      ? new Date(start) : start;
    var endDate = (typeof end === "string")
      ? new Date(end) : end;
    return (curDate > startDate) && (curDate < endDate);
  };
}

Usage.

With the help of the helper function, we can then pretty easily filter the "current" dates:

// Get the list of (date string) objects.
var allDates = data.period.startend;

// Capture the current date, returning the date range comparator.
var comparator = includesNow();

// Get the list of those (date string) objects `obj`
// that satisfy `comparator(obj.startDate, obj.endDate) === true`.
var currentDates = allDates.filter(function(obj) {
  return comparator(obj.startDate, obj.endDate);
});

// This is a function of current date, so will be empty at some point.
currentDates[0];
// => Object {startDate: "2015-11-17 15:43:37", endDate: "2015-11-18 19:43:37"}

If you know your objects will always be Strings and never actual Date objects, then you can simplify includesNow considerably. If you're interested in the closed range be sure to replace > and < with ≥ and ≤, respectively.

edited Nov 18, 2015 at 2:59

answered Nov 18, 2015 at 1:13

Hunan Rostomyan

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6 Comments

Harry Over a year ago

So I replace my for loop with this? Tried but won't run. My bad luck or I'm getting it wrong?

Harry Over a year ago

Thanks much Hunan for your input. How do I finally utilize it with my if else statement to yield the right alert?

Hunan Rostomyan Over a year ago

@Harry First, replace the lines that declare curDate and datetime with var comparator = includesNow(). Then inside the conditional, instead of datetime > obj.startDate && datetime < obj.endDate do comparator(obj.startDate, obj.endDate).

Harry Over a year ago

Hunan, I feel silly for making you crazy and bother you again, but I did exactly as you guided but still not getting results. Following is how my code looks like now.

Harry Over a year ago

function includesNow() { 		  var curDate = new Date(); 		  return function(start, end) { 			var startDate = (typeof start === "string") 			  ? new Date(start) : start; 			var endDate = (typeof end === "string") 			  ? new Date(end) : end; 			return (curDate > startDate) && (curDate < endDate); 		  }; 		}  		var allDates = data.period.startend;  		var comparator = includesNow();  		var currentDates = allDates.filter(function(obj) { 		  return comparator(obj.startDate, obj.endDate); 		  });  		if (comparator(obj.startDate, obj.endDate)){ 					alert('w'); 				} else { 					alert('n'); 				}

|

Exziled · Accepted Answer · 2015-11-18 01:08:16Z

0

JSON date is not a date object. It's a string. You're trying to compare a Date obj to a String.

If the JSON date was an ISO formatted date you could do :

var dateStr = JSON.parse(date);
var realDate = new Date(dateStr);

realDate would now have a js date object. Unfortunately in your example the startDate and endDate are not ISO strings.

This would be the easiest/cleanest solution. Otherwise you could always get the JSON date strings and break them apart with substring() and convert the years/months/days with Number(); and then compare them that way?

answered Nov 18, 2015 at 1:08

Exziled

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