Osada Vidath Chandrasekara
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Schedule Cron Jobs Easily And Conveniently With Agenda

Schedule Cron Jobs Easily And Conveniently With Agenda

Osada Vidath Chandrasekara
ยทMar 26, 2022ยท

4 min read

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Table of contents

  • Introduction ๐ŸŽ‰
  • Getting Started โœจ
  • Scheduling Jobs โš’๏ธ
  • Time To Test ๐Ÿงช
  • Links ๐Ÿ”—

When it comes to building serious applications, at some point you'll need to schedule some cron jobs. It might be to send a scheduled email, schedule to tweet something or even schedule to post something.

There is a handful of ways you can achieve something like that but today we are gonna take a look at my favourite which is the Agenda library.

Introduction ๐ŸŽ‰

Agenda is a lightweight job scheduling library for Node.js as they say on their ReadMe. By using agenda you can create, manage cron jobs. It also allows you to use a MongoDB database to store your jobs so that your cron jobs will be persisted even if you restart the server.

Getting Started โœจ

First, initialize a node project with npm init -y or yarn init -y. Then you will need to install a couple of dependencies. We will need Express, Agenda and DayJS. I will explain what each of them is for later. For now, just install them with npm install express agenda dayjs or yarn add express agenda dayjs.

I am gonna use import syntax for the rest of the tutorial. If you also need to use important statements make sure to add "type": "module" to your package.json file

In the index.js file, you can import all of your modules and initialize an express app like follows.

import express from "express";
import Agenda from "agenda";
import dayjs from "dayjs";

const app = express();

Make sure to listen to a specific port at the bottom of your file. In this case, I am gonna listen on port 3000.

app.listen(3000);

Then you can initialize an Agenda instance and pass the database connection URL and the collection name. I am gonna pass my local MongoDB database URL and the collection name is agendaJobs. You can choose whatever name you want.

const agenda = new Agenda({
  db: {
    address: "mongodb://localhost:27017/agenda-test",
    collection: "agendaJobs",
  },
});

Then you need to start the Agenda instance. To do that update your express listen statement like this.

app.listen(3000, () => {
  agenda.start();
});

It will start the agenda instance once express initialized and it is listening on the specified port. Now express and agenda are fully configured and ready to go.

Scheduling Jobs โš’๏ธ

Before scheduling a job, you need to define a job. This definition includes what the job does when it is called. You can define a job as follows.

agenda.define("doSomething", (job) => {}

You can give any name to your job. This name will be important when you want to schedule it. For now, I am gonna console log something when the job runs.

agenda.define("doSomething", (job) => {
  console.log("Job Ran");
});

Now you need a way to test this out. For this, I am gonna create an express endpoint.

app.get("/", async (req, res) => {
  const data = await agenda.schedule(
    dayjs().add(5, "seconds").format(),
    "doSomething"
  );

  res.json(data);
});

What we're doing here is scheduling a job to run in 5 seconds. We are using dayjs to add 5 seconds to the current time. You can see that the job is scheduled and the job details are returned.

Time To Test ๐Ÿงช

If everything went fine, we should see,

  1. Job Details in the response.
  2. A brand new record in the database.
  3. Terminal output in 5 seconds.

First, run your app with nodemon command. Then you can make a get request to http://localhost:3000/ with any method you want. In this case, I am gonna use Hoppscotch.

Once you have sent the request, if everything is successful, you will receive a response with the job details like this.

{
  "name": "doSomething",
  "data": {},
  "priority": 0,
  "type": "normal",
  "nextRunAt": "2022-03-26T07:38:21.009+00:00",
  "_id": "623ec2e8fdced2c3bd29695b"
}

And if you check your database you will see the created job's record like this image.png

After exactly 5 seconds, you should see the following output in the terminal.

Terminal Output

Most importantly the job will persist even if you restart the server. So that is it for the basic Agenda tutorial. I hope you learnt something and I am also planning to do a more in-depth tutorial on how to use Agenda. Let me know what do you think.

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