How to set endDate to tomorrow in litepicker.js

you can add a function for this.

function addDays(days) {
  let result = new Date();
  result.setDate(result.getDate() + days);
  return result;
}

so the final code looks like this.

function addDays(days) {
  let result = new Date();
  result.setDate(result.getDate() + days);
  return result;
}

const picker = new Litepicker({
    element: document.getElementById('start-date'),
    elementEnd: document.getElementById('end-date'),
    singleMode: false,
    allowRepick: true,
    format: 'D MMMM YYYY',
    startDate: new Date(),
    endDate: addDays(1),
    numberOfMonths: 1,
    numberOfColumns: 1,
    tooltipText: {
        one: 'night',
        other: 'nights'
    },
    tooltipNumber: (totalDays) => {
        return totalDays - 1;
    }
});

this should also take care of the changing month.