Introduction

Ever wanted to do specific things on your application server at certain times without having to manually run them yourself? This is where scheduled tasks come in handy.

In this article, you'l create scheduled tasks in Node applications using the node-cron module. You’ll schedule the execution of different scripts at different intervals from your application.

In this tutorial you’ll build a small application that automatically deletes auto-generated log files from the server. Then you’ll look at a few additional use cases.

Prerequisites

To follow through this tutorial, you’ll need:

• A local development environment for Node.js. Follow How to Install Node.js and Create a Local Development Environment

Step 1 – Creating A Node Application and Installing Dependencies

To get started, create a new Node application by opening your terminal and creating a new folder for your project.

 mkdir cron-jobs-node && cd cron-jobs-node

Then initialize it, which creates a package.json file which you’ll use to track dependencies:

npm init -y

Add the express web framework as a dependency, as well as the node-cron and the fs modules by running the following command:

 npm install express node-cron fs

The express module powers the web server you’ll build. node-cron is the task scheduler, and fs is the Node file system module.

The dependencies are installed; let’s build the server.

Step 2 – Building the Backend Server

Create an index.js file and then import the necessary node modules:

nano index.js

Add this code to index.js to include node-cron and express and create an instance of Express:

const cron = require("node-cron");
const express = require("express");
const fs = require("fs");

app = express();

This application will generate logs, and after a while, you’ll want to delete the error log files at intervals automatically. You’ll use node-cron to do this.

To see how this module works, add the following to your index.js file which displays a message every minute:

    // schedule tasks to be run on the server   
    cron.schedule("* * * * *", function() {
      console.log("running a task every minute");
    });

    app.listen(3128);

Now, when you run the server, we get the following result:

node index.js

Output
running a task every minute
running a task every minute

You have a task running every minute. Stop the server with CTRL+C.

Now let’s look at how to run tasks in more detail.

Step 2 – Scheduling Tasks at Different intervals

With node-cron, you can schedule tasks for different intervals.

In the previous example, you created a job that ran every minute by passing * * * * * to the schedule function. Each of those asterisks has a special meaning:

     * * * * * *
     | | | | | |
     | | | | | day of week
     | | | | month
     | | | day of month
     | | hour
     | minute
     second ( optional )

Learn more about how this notation works in How To Use Cron to Automate Tasks on a VPS.

To delete the log file from the server on the 21st of every month, update the index.js to look like this:

    // schedule tasks to be run on the server
    cron.schedule("* * 21 * *", function() {
      console.log("---------------------");
      console.log("Running Cron Job");
      fs.unlink("./error.log", err => {
        if (err) throw err;
        console.log("Error file successfully deleted");
      });
    });

    app.listen("3128");

Now, when the server is run, you’ll get the following output on the 21st of the month:

To simulate this yourself, change the scheduler to run in a shorter interval.

You can run any actions inside the scheduler. Actions ranging from creating a file, to sending emails and running scripts. Let’s take a look at more use cases

Use Case: Backing Up Databases

Ensuring the accessibility of user data is very key to any business. If an unforeseen event happens and your database becomes corrupted or damaged, you’ll need to restore your database from a backup. You’ll be in serious trouble if you don’t have any form of existing backup for your business. You can use what you’ve learned so far to periodically backup the existing data in your database. Let’s take a look at how to do this. In this example, you’ll use the SQLite database, as it’s less complex than other options and works in the context of this example.

Visit the SQLite3 download page to download SQlite3 for your platform. You can also install SQlite3 on Ubuntu with the following commands:

sudo apt-get update
sudo apt-get install sqlite3 libsqlite3-dev

Next, install a Node module that lets your app run shell scripts:

You’ll use this library to execute a command that exports your data.

Now create a sample database by running the command:

sqlite3 database.sqlite

To backup your database at 11:59pm every day, update your index.js file to look like this:

    const fs = require("fs");
    let shell = require("shelljs");
    const express = require("express");

    app = express();

    // To backup a database
    cron.schedule("59 23 * * *", function() {
      console.log("---------------------");
      console.log("Running Cron Job");
      if (shell.exec("sqlite3 database.sqlite  .dump > data_dump.sql").code !== 0) {
        shell.exit(1);
      }
      else{
        shell.echo("Database backup complete");
      }
    });
    app.listen("3128");

Save the file and run your server:

 node index.js

You’ll see the following results:

Next, let’s look at sending periodic emails.

Use Case: Sending Scheduled Emails

You can also use jobs to keep your users up to date by sending them emails at different intervals. For example, you can curate a list of interesting links and then send them to users every Sunday. To do this, use the nodemailer module and connect it to your SMTP server, like GMail.

Install nodemailer by running the command:

 npm install --save nodemailer

Once that is done, update the index.js file to add a section that defines the mailer and sets the username and password for a GMail account:

    const cron = require("node-cron");
    const express = require("express");
    let nodemailer = require("nodemailer");

    app = express();

    // create mail transporter
    let transporter = nodemailer.createTransport({
      service: "gmail",
      auth: {
        user: "your_email_address@gmail.com",
        pass: "your_password"
      }
    });

Warning: You will need to temporarily allow non-secure sign-in for your Gmail account if you’d like to use it for testing purposes here. For production applications, configure a specific secure Email account and use those credentials.

Then add the task to send the messages every Wednesday:

    // sending emails at periodic intervals
    cron.schedule("* * * * Wednesday", function(){
      console.log("---------------------");
      console.log("Running Cron Job");
      let mailOptions = {
        from: "COMPANYEMAIL@gmail.com",
        to: "sampleuser@gmail.com",
        subject: `Not a GDPR update ;)`,
        text: `Hi there, this email was automatically sent by us`
      };
      transporter.sendMail(mailOptions, function(error, info) {
        if (error) {
          throw error;
        } else {
          console.log("Email successfully sent!");
        }
      });
    });

    app.listen("3128");

Now, when you run the server using the command node index.js , you get the following result:

Conclusion

In this article, you used node-cron to schedule jobs in your Node.js applications. You can find the code examples for this tutorial in this GitHub repository repository.