How to set up Scheduled Functions with NodeJs, Express and Node-Cron

Step 1: Create a NodeJs application.

Initialize a new app with npm and install the Express package. Make sure NodeJs is installed on your machine.

- npm init

- npm i express

Step 2: Set up the Express server

- Create the app.js file (note that some people prefer to call this file server.js)

- Configure the port and set up the listener

const express = require("express");
const app = express();
app.set("port", process.env.PORT || 3000);

app.listen(app.get("port"), () => {
  console.log("Express server listening on port " + app.get("port"));
});

Step 3: Add the node-cron npm package to the application

- npm i node-cron

Step 4: Set up a folder for your scheduled jobs

- Create a folder called "scheduledFunctions" or similar

Step 5: Define the logic to run your scheduled jobs

- In the folder you just set up, create a file to hold your scheduled function logic. You can also use different files for each task if you prefer.

- Configure scheduled logic

const CronJob = require("node-cron");

exports.initScheduledJobs = () => {
  const scheduledJobFunction = CronJob.schedule("*/5 * * * *", () => {
    console.log("I'm executed on a schedule!");
    // Add your custom logic here
  });

  scheduledJobFunction.start();
}

The execution frequency of your custom function is defined as the first argument to the Cron.schedule function. Note that this argument is written as a Cron Schedule Expression or crontab. I find Crontab Guru a really useful resource to play around and get comfortable with schedule expressions so you can easily set up your own.

Step 6: Configure the Express app to initialise and run the job schedules

- In the app.js file add a call to the init function(s) from your scheduled file(s).

const express = require("express");
// DEFINE the path to your scheduled function(s)
const scheduledFunctions = require('./scheduledFunctions');
const app = express();
app.set("port", process.env.PORT || 3000);

// ADD CALL to execute your function(s)
scheduledFunctions.initScheduledJobs();

app.listen(app.get("port"), () => {
  console.log("Express server listening on port " + app.get("port"));
});

Start the app to generate the functions and their schedules in the Cron scheduler. Your custom logic will be executed to schedule as long as the app is running.