How to send automated email in node js 24hours before a fixed date?

Question

I want to implement a setup in my node app where the server can send emails to a number of people 24hrs before a specific date. This date is coming from DB.

For example: The date is 25th December, so I need my server to send mails to a group of clients on 24th December. How do I code it today such that it will send the mail in future?

(My node app is hosted on a VPS so it will be running always.)

Answer 1

You can use the node-schedule modules. https://www.npmjs.com/package/node-schedule

var schedule = require('node-schedule');
var date = new Date(2020, 12, 24, 5, 30, 0);

var j = schedule.scheduleJob(date, function(y){ });

Or you can do it the old fashioned way. Something like.

const then = "2020-12-24 05:00:00";

const inter = setInterval(() => {
    const now = new Date();
    if (Date.parse(now) > Date.parse(then)) {
       clearInterval(inter);
    }
}, 1000 * 60 * 60 );

Edit:

You could have something like.

const schedules = {};

function dbUpdate() {
    const somedate = new Date();
    const userid = getUpdatedUser();
    cancelSchedule(userid);
    createSchedule(userid, somedate);
}

function createSchedule(userid, somedate) {
    const date = new Date(somedate);
    schedules[userid] = schedule.scheduleJob(date, function(y){ });
}

function cancelSchedule(userid) {
    schedules[userid].cancel();
}

Not tested but something along these line