Shannon Hochkins Shannon Hochkins - 1 year ago 109
Javascript Question

How can I run a function at specific time & date?

How can run a function at a given time and date.

Example, I have a function that on the 12th of each month at 10AM, I have a surprise, and I want to tell them this. How can I always have this function running, but only execute at that time?

This page will be running 24/7, as pointed out, apparently this can effect my answer.

Obviously I'd have to compare against the current date, but I'm not sure how to check if the current date and time has been matched.


Answer Source

It's not advised to use setInterval because it has non-deterministic behaviour - events can be missed, or fire all at once. Time will fall out of sync, too.

The code below instead uses setTimeout with a one minute period, where each minute the timer is resynchronised so as to fall as closely to the hh:mm:00.000s point as possible.

function surprise(cb) {
    (function loop() {
        var now = new Date();
        if (now.getDate() === 12 && now.getHours() === 12 && now.getMinutes() === 0) {
        now = new Date();                  // allow for time passing
        var delay = 60000 - (now % 60000); // exact ms to next minute interval
        setTimeout(loop, delay);
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