Incrementing an ISO date string in JavaScript (e.g. '2014-03-30' -> '2014-03-31')

Question

My question is similar to this one, but I need to process ISO strings.

I've tried to adapt the solution from the other question:

var getNextDay = function(day) {
    var date = new Date(day);
    date.setDate(date.getDate() + 1);
    return date.toISOString().slice(0, 10);
};

This actually works in most cases, e.g. getNextDay('2014-03-31') returns '2014-04-01'.

However, getNextDay('2014-03-30') gives me '2014-03-30' (The full string before slicing is '2014-03-30T23:00:00.000Z')

Does anyone know why this happens and how to solve it?

Answer 1

This is caused by Daylight saving adjustment that happened on that date. March 30, 2014: Europe starts Daylight Saving Time

Fix it by using UTCDate instead:

var getNextDay = function(day) {
    var date = new Date(day);
    date.setUTCDate(date.getUTCDate() + 1);
    return date.toISOString().slice(0, 10);
};