In this article, we will see what are job schedulers and how to implement the job schedulers in nodejs. Implementing Job Schedulers in Node.js

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Ever wondered how the application server back up the files periodically without any physical interruption. This is where Cron jobs come in.

Cron Jobs schedules a job periodically to do the actions that are configured to do.

there are few use cases where cron jobs play a vital role. they are,

Deleting Log files - Application generates a lot of logs.clearing old logs will save lots of space in the server. it can be done using cron jobs.
DB Backup - Database backup saves the application from disasters. Cron job will be helpful to do that.
Application Logic - we can use cron jobs to do some application logic on a time basis.

How cron job works

we will write a cron job to archive the old records in the database in a production application.

Firstly, create a project and install the following dependencies,

npm init --yes
npm install express node-cron mongoose faker

express - web server library in nodejs
node-cron - cron job scheduler library in nodejs
mongoose - ORM for MongoDB

After that, create a file called Model.js and add the following code

const mongoose = require('mongoose');

const weatherSchema = new mongoose.Schema({
    minTemp : {
        type: Number
    },
    maxTemp : {
        type : Number
    },
    recordedDate : {
        type : Date
    },
    isArchived : {
        type : Boolean,
        default : false
    }
});

class Weather {

    static getRec(date) {
        return this.find({
            recordedDate : {
                '$lte' :new Date(date)
            }
        }).exec();
    }

    static insertBulkData(data){
        return this.insertMany(data);
    }

    static archiveData(date){
        
        return this.updateMany({
            recordedDate : {
                '$lte' :new Date(date)
            }
        },{
            $set : {
                isArchived : true
            }
        }).exec();
    }

    static getArchivedData(){
        return this.find({
            isArchived : true
        }).exec();
    }
}

weatherSchema.loadClass(Weather);

module.exports = mongoose.model('Weather',weatherSchema)

Mainly, Model.js creates a mongoose schema for a DB table which stores the weather data in the database.

After that, create a file called scheduler.js and add the code for job scheduler.

cron.schedule("* * * * * *",() => {
    console.log("Running every minute");
})

cron schedule schedules the job for time format that is mentioned.

To learn more about cron job format, there is a great site crontab-guru which explains in detail

Connect the mongoose with the Express to insert some dummy data to database.

const cron = require('node-cron');
const express = require('express');
const mongoose = require('mongoose');
const app = express();
const faker = require('faker');
const model = require('./Model');


mongoose.connect('mongodb://localhost:27017/nodescheduler').then((res) => {

    console.log('mongoose connected successfully');

    app.get("/insertdata",async (req,res) => {
        let data = [];
        for(let i=0;i < 100;i++){
            let record = {
                minTemp: faker.random.number(),
                maxTemp : faker.random.number(),
                recordedDate : faker.date.past()
            }
            data.push(record);
        }

        await model.insertBulkData(data);

        res.send("Data is inserted");
    })

    app.listen(4000,() => {
        console.log("Server is running port 4000");
    })
    

})
.catch((err) => {
    console.error(err);
})

To insert some dummy data using fakerjs. run the script with the command, and visit the URL http://localhost:4000/insertdata

node scheduler.js

it will create some bulk dummy data to test the job scheduler. Now it is time to add the job scheduler.

cron.schedule("* * * * */3 *",async() => {

    var d = new Date();
    d.setMonth(d.getMonth() - 2); //1 month ago
    
    await model.archiveData(d);

    console.log("scheduler => archived");  
})

Above cron job will run every 3 months, to mark the data as archived in the database.

Likewise, we can use cron jobs to schedule a job for our application logics.

Summary

Above all, cron jobs play a vital role in some application development use cases. it is always good to know how cron jobs work in application development.

If you want to implement job scheduler in a production level standard with minimal effort, I recommend you to check out bree

Reference : https://crontab.guru