How to configure a cron job to run every other week on a certain day

[mohammedmulazada]

Hello!

The title gives it away, but I am looking on how to configure the cron jobs to run every other week on a certain day.
I googled quite a bit and found answers that seemed like they would work, but still seems like it triggers more often than I would like it to. I tried with this CRON:

const job = Cron("40 9 7-14,22-28 * 1", (job) => {});
console.log(job.nextRuns(10));

And it gave me back:

  2023-03-20T08:40:00.000Z,
  2023-03-22T08:40:00.000Z,
  2023-03-23T08:40:00.000Z,
  2023-03-24T08:40:00.000Z,
  2023-03-25T08:40:00.000Z,
  2023-03-26T07:40:00.000Z,
  2023-03-27T07:40:00.000Z,
  2023-03-28T07:40:00.000Z,
  2023-04-03T07:40:00.000Z,
  2023-04-07T07:40:00.000Z

But what I want is for it to trigger every second week on a Monday like so:

  2023-03-20T08:40:00.000Z,
  2023-04-03T08:40:00.000Z,
  2023-04-17T08:40:00.000Z,
  2023-05-01T08:40:00.000Z,
  2023-05-15T08:40:00.000Z,
  2023-05-29T07:40:00.000Z,
  2023-06-12T07:40:00.000Z,
  2023-06-26T07:40:00.000Z,
  2023-07-10T07:40:00.000Z,
  2023-07-24T07:40:00.000Z

Is it possible to do this with the library? BTW other than me getting stuck on this the library is excellent! Thanks for making & maintaining it :)

[Hexagon]

It isn't possible by using a cron expression alone, as the aspect of weeks isn't included in the pattern. So you'll have to make use of some library features 😄

Continuing on your solution where the job is executed between dates 7-14.22-28 every months, you'll have to disable legacyMode.

By default cron uses OR to combine day of month with day of week, making the expression execute every mondag AND day 7-14 and 22-28.

legacyMode: false changes this behavior to AND.

This should work better:

const job = Cron("40 9 7-14,22-28 * 1", { legacyMode: false}, (job) => {});
console.log(job.nextRuns(10));

Another way would be to use a minimum interval between executions, which is larger than one week. Since you want it to execute 00:09:40, on mondays, the cron expression should look something like 0 40 9 * * 1, combining that with interval: 60 * 60 * 24 * 8 would give expected result. Only downside with this is that the week of execution could change if you restart the application

const job = Cron("0 40 9 * * 1", { interval: 60 * 60 * 24 * 8 }, (job) => {});
console.log(job.nextRuns(10));

Another option is to always run on mondays, and use an additional check inside the triggered function, to check for odd or even week numbers.

const job = Cron("0 40 9 * * 1", (job) => { 
// Check if week number is even or odd.. This is not trivial though
if(weekIsEven) {
   dostuff();
}
});

console.log(job.nextRuns(10)); // will show every monday, but will only trigger every other