Generating a collection of timestamps for dates with a yearly increment

Question

Generating a collection of timestamps for dates with a yearly increment

Consider pulling the minimum date as 1420070400000, which corresponds to 2015-01-01 00:00:00, and the maximum date as 1575158400000, which translates to 2019-12-01 00:00:00.

Next, establish an array of timestamps for each month between those two dates using this script:

var offset = 5*60*60000

dtMin = new Date(+1420070400000 + offset);
dtMax = new Date(+1575158400000 + offset);

console.log("dtmin: ", dtMin);
console.log("dtmax: ", dtMax);

while (dtMin <= dtMax) {

  dtRng.push((dtMin.getTime() - offset).toString());

  dtMin = new Date(new Date(dtMin).setMonth(dtMin.getMonth()+1));

}

console.log("dt rng:", JSON.stringify(dtRng));

The resulting array looks like this:

["1420070400000","1422748800000","1425168000000","1427842800000","1430434800000","1433113200000","1435705200000","1438383600000","1441062000000","1443654000000","1446332400000","1448928000000","1451606400000","1454284800000","1456790400000","1459465200000","1462057200000","1464735600000","1467327600000","1470006000000","1472684400000","1475276400000","1477954800000","1480550400000","1483228800000","1485907200000","1488326400000","1491001200000","1493593200000","1496271600000","1498863600000","1501542000000","1504220400000","1506812400000","1509490800000","1512086400000","1514764800000","1517443200000","1519862400000","1522537200000","1525129200000","1527807600000","1530399600000","1533078000000","1535756400000","1538348400000","1541026800000","1543622400000","1546300800000","1548979200000","1551398400000","1554073200000","1556665200000","1559343600000","1561935600000","1564614000000","1567292400000","1569884400000","1572562800000","1575158400000"]

However, sometimes it includes a 31-day or 30-day interval such as:

Epoch date  Human readable date (GMT) 
1420070400  2015-01-01 00:00:00
1422748800  2015-02-01 00:00:00
1425168000  2015-03-01 00:00:00
1427842800  2015-03-31 23:00:00
1430434800  2015-04-30 23:00:00
1433113200  2015-05-31 23:00:00
1435705200  2015-06-30 23:00:00
1438383600  2015-07-31 23:00:00

If you're incrementing by month, why is this happening?

Moreover, keep in mind that minDate and maxDate can fluctuate. For example, minDate could be 1464739200000 (Wed, 01 Jun 2016 00:00:00) while maxDate might be 1488326400000 (Wed, 01 Mar 2017 00:00:00)...

Also, why does it work correctly for the initial 3 months but not thereafter? The behavior seems erratic...

---EDIT-----

Considering using moment.js for this purpose, you can update the while section with the following code:

   while (dtMin <= dtMax) {

       dtRng.push(dtMin);

       dtMin = moment(dtMin).add(1, 'months').toDate();
       console.log("dtmin: ", dtMin);
   }

An unexpected outcome occurs here...the console displays:

Sun Feb 01 2015 00:00:00 GMT-0500 (EST)
Sun Mar 01 2015 00:00:00 GMT-0500 (EST)
Wed Apr 01 2015 00:00:00 GMT-0400 (EDT)
Fri May 01 2015 00:00:00 GMT-0400 (EDT)
Mon Jun 01 2015 00:00:00 GMT-0400 (EDT)
Wed Jul 01 2015 00:00:00 GMT-0400 (EDT)
Sat Aug 01 2015 00:00:00 GMT-0400 (EDT)
Tue Sep 01 2015 00:00:00 GMT-0400 (EDT)

Nevertheless, the timestamps pushed to dtRng look different, showing 30th and 31st days with 23 hours:

Epoch date  Human readable date (GMT) 
1422748800  2015-02-01 00:00:00
1425168000  2015-03-01 00:00:00
1427842800  2015-03-31 23:00:00
1430434800  2015-04-30 23:00:00
1433113200  2015-05-31 23:00:00
1435705200  2015-06-30 23:00:00
1438383600  2015-07-31 23:00:00
1441062000  2015-08-31 23:00:00
1443654000  2015-09-30 23:00:00

The expected output should appear like this:

Epoch date  Human readable date (GMT) 
1422748800  2015-02-01 00:00:00
1425168000  2015-03-01 00:00:00
1427846400  2015-04-01 00:00:00
1430438400  2015-05-01 00:00:00
1433116800  2015-06-01 00:00:00
1435708800  2015-07-01 00:00:00
1438387200  2015-08-01 00:00:00
1441065600  2015-09-01 00:00:00

javascript arrays datetime

Answer 1

Answer №1

It appears that there is a time zone complication where transitioning from Eastern Standard Time (EST) to Eastern Daylight Time (EDT) results in either losing or gaining an hour, leading to the display of 23:00:00 for certain dates.

While handling time zones can be tricky, I recommend a straightforward solution for this issue by generating all dates in UTC using the Date.UTC function. A simple loop can be implemented to iterate through each month for every year:

for(var year = 2015; year < 2020; year++)
    for(var month = 0; month < 12; month++)
        dtRng.push(new Date(Date.UTC(year, month, 1, 00, 00, 00)));

The output obtained from

console.log(JSON.stringify(dtRng))

provides accurate results:

"2015-02-01T00:00:00.000Z",
"2015-03-01T00:00:00.000Z",
"2015-04-01T00:00:00.000Z",
"2015-05-01T00:00:00.000Z",
"2015-06-01T00:00:00.000Z",
....

An adjustment could involve segmenting the loop into three parts for start and end dates:

For the initial year, loop through months starting from the specified month to December.
For all years except the final one, loop through all twelve months.
For the last year, loop through January to the ending month.

The following code demonstrates this logic for a date range (2015/03/01 to 2019/09/01) formatted as YYYY/MM/DD.

// Setting up the date range.
var startYear = 2015, startMonth = 03,
      endYear = 2019,   endMonth = 09;

// Iterating through the years.
for(var year = startYear; year <= endYear; year++) {
    var currStartMonth = 1, currEndMonth = 12;

    // Skipping months before the date range in the initial year.
    if (year === startYear) currStartMonth = startMonth;

    // Skipping months after the date range in the final year.
    // This also handles cases when startYear is equal to endYear.
    if (year === endYear)     currEndMonth = endMonth;

    // Looping through months and adding them to the dates array.
    // '- 1' is used due to the zero-based indexing of months.
    for (var month = currStartMonth - 1; month < currEndMonth; month++) 
        dtRng.push(new Date(Date.UTC(year, month, 1, 00, 00, 00)));
}

Answer 2

It appears that there is a time zone complication where transitioning from Eastern Standard Time (EST) to Eastern Daylight Time (EDT) results in either losing or gaining an hour, leading to the display of 23:00:00 for certain dates.

While handling time zones can be tricky, I recommend a straightforward solution for this issue by generating all dates in UTC using the Date.UTC function. A simple loop can be implemented to iterate through each month for every year:

for(var year = 2015; year < 2020; year++)
    for(var month = 0; month < 12; month++)
        dtRng.push(new Date(Date.UTC(year, month, 1, 00, 00, 00)));

The output obtained from

console.log(JSON.stringify(dtRng))

provides accurate results:

"2015-02-01T00:00:00.000Z",
"2015-03-01T00:00:00.000Z",
"2015-04-01T00:00:00.000Z",
"2015-05-01T00:00:00.000Z",
"2015-06-01T00:00:00.000Z",
....

An adjustment could involve segmenting the loop into three parts for start and end dates:

For the initial year, loop through months starting from the specified month to December.
For all years except the final one, loop through all twelve months.
For the last year, loop through January to the ending month.

The following code demonstrates this logic for a date range (2015/03/01 to 2019/09/01) formatted as YYYY/MM/DD.

// Setting up the date range.
var startYear = 2015, startMonth = 03,
      endYear = 2019,   endMonth = 09;

// Iterating through the years.
for(var year = startYear; year <= endYear; year++) {
    var currStartMonth = 1, currEndMonth = 12;

    // Skipping months before the date range in the initial year.
    if (year === startYear) currStartMonth = startMonth;

    // Skipping months after the date range in the final year.
    // This also handles cases when startYear is equal to endYear.
    if (year === endYear)     currEndMonth = endMonth;

    // Looping through months and adding them to the dates array.
    // '- 1' is used due to the zero-based indexing of months.
    for (var month = currStartMonth - 1; month < currEndMonth; month++) 
        dtRng.push(new Date(Date.UTC(year, month, 1, 00, 00, 00)));
}

Generating a collection of timestamps for dates with a yearly increment

Answer №1

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