sectom/functions/isBST.js

Sectom is a useful npm package that has multiple easy to use functions.

function lastSunday2(month, year) {
  var d = new Date();
  var lastDayOfMonth = new Date(
    Date.UTC(year || d.getFullYear(), month + 1, 0)
  );
  var day = lastDayOfMonth.getDay();
  return new Date(
    Date.UTC(
      lastDayOfMonth.getFullYear(),
      lastDayOfMonth.getMonth(),
      lastDayOfMonth.getDate() - day
    )
  );
}

/**
 * Checks if it is currently British Summer Time or not
 * @param {Date} date
 *
 */
function isBST(date = undefined) {
  var d = date || new Date();
  var starts = lastSunday2(2, d.getFullYear());
  starts.setHours(1);
  var ends = lastSunday2(9, d.getFullYear());
  starts.setHours(1);
  return d.getTime() >= starts.getTime() && d.getTime() < ends.getTime();
}

module.exports = isBST;