PaulH

Most recent activity

• How to set the timezone on the Pico

  in JavaScript • 5 years, 6 months

  

  Maybe this could help others searching for DST stuff (for Europe at least):

  
  var offsetUTC = 1; // the offset to UTC in Standard Time (winter)
  var useDST = true; // if true, DST will be taken into account when setting TZ
  
  // these formulae are valid until 2099 (or 2022  https://en.wikipedia.org/wiki/Summer_tim­e_in_Europe
  function dayEndWinter(year) { // last Sunday of March
          return Math.ceil(31 - ((((5 * year) / 4) + 4) % 7));
  }
  
  function dayEndSummer(year) { // last Sunday of October
          return Math.ceil(31 - ((((5 * year) / 4) + 1) % 7));
  }
  
  function checkDST(date) {
  
          let year = date.getFullYear();
          let dateStart = new Date(`${year}-03-${dayEndWinter(year)}T0­1:00:00 GMT`);
          let dateEnd = new Date(`${year}-10-${dayEndSummer(year)}T0­1:00:00 GMT`);
    
          return (date >= dateStart && date < dateEnd);
    
  }
  
  function setTimeZone(offsetUTC, useDST) {
          E.setTimeZone(0); // start with UTC
          if (useDST && checkDST(new Date())) {
              offsetUTC += 1; // we're in DST
          }
          E.setTimeZone(offsetUTC);
          console.log('Time after setting TZ: ' + (new Date()).toString());
  }
  
  // sets the TZ with respect to DST
  setTimeZone(offsetUTC, useDST);
  
  // get some start and end dates
  for (let y=2018;y<2023;y++) {
          let dateStart = new Date(`${y}-03-${dayEndWinter(y)}T01:00:0­0 GMT`);
          let dateEnd = new Date(`${y}-10-${dayEndSummer(y)}T01:00:0­0 GMT`);
          console.log(dateStart.toUTCString() + ' till ' + dateEnd.toUTCString());
  }
  
  // test some dates
  let dateStrings = [
          '2019-01-01T00:01:00 GMT', // DST false
          '2019-03-31T00:01:00 GMT', // DST false
          '2019-03-31T02:01:00 GMT', // DST true
          '2019-08-01T00:01:00 GMT', // DST true
          '2019-10-27T00:01:00 GMT', // DST true
          '2019-10-27T01:01:00 GMT', // DST false
          '2019-12-01T00:01:00 GMT', // DST false
  ];
  dateStrings.forEach(function (dateString) {
          let date = new Date(dateString);
          console.log('Checking date ' + date.toString() + ': ' + checkDST(date));
  })