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Jayant
Jayant

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Cron Jobs in Nest JS

#nestjs #backend #scheduledtasks #learning

Cron Jobs are scheduled Tasks that runs automatically at a specified time.
They are commonly used for these works.

  • Running Backups at MIDNIGHT
  • Sending Email Reports

They use Cron Expressions that defines when the job should run.

// Format - they are either 5 or 6 fields * * * * * * │ │ │ │ │ │ │ │ │ │ │ └─ Day of Week (0 - 6) (Sunday to Saturday) │ │ │ │ └────── Month (1 - 12) │ │ │ └──────────── Day of Month (1 - 31) │ │ └────────────────── Hour (0 - 23) │ └──────────────────────── Minute (0 - 59) └────────────────────────────── (optional) Seconds (0 - 59)
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To make a Cron Expression you can go to Cron Tab Guru.

* * * * * * - RUNS EVERY Seconds * * * * * 1 - RUNS EVERY Second on Monday 0 1 * * * 1 - RUNS at past midnight every Monday 0 */1 * * * 1 - RUNS every 1 minute on Monday
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we don't need to memorize them, we can use Corn Expression Enums to make it easier.

How & Where to Run it

we can run it in our server or we can use serverless Cron Jobs provided by Cloud Providers.

To Run Cron Job in Node.js

// In Express // Install the `node-cron` package import cron from 'node-cron'; cron.schedule('0 0 * * *', () => { console.log('Running task at midnight'); }); // In NestJS // install @nestjs/schedule package // Inside app.module register your Schedule Module, it initialize and registers any cron job in our app, import { Module } from '@nestjs/common'; import { ScheduleModule } from '@nestjs/schedule'; @Module({ imports: [ ScheduleModule.forRoot() ], }) export class AppModule {} // To create a Cron JOb we need to attach @Cron() decorator to the handler // Using CronExpressionEnums import { Injectable, Logger } from '@nestjs/common'; import { Cron, CronExpression } from '@nestjs/schedule'; @Injectable() export class TasksService { private readonly logger = new Logger(TasksService.name); @Cron(CronExpression.EVERY_30_SECONDS) handleCron() { this.logger.debug('Called every 30 seconds'); } } // If any exception occurs it will be logged in the console, as every method annoted with @Cron is automatically wrapped in try-catch block. // We can also gives additional options to the @Cron decorator import { Injectable, Logger } from '@nestjs/common'; import { Cron, CronExpression } from '@nestjs/schedule'; @Injectable() export class TasksService { private readonly logger = new Logger(TasksService.name); @Cron(CronExpression.EVERY_30_SECONDS, { name: 'my-cron-job', timeZone: 'Asia/Kolkata', }) handleCron() { this.logger.debug('Called every 30 seconds'); } }
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In NestJS we can access the cron job once it is declared & also create it dynamically.

If we want to control a cron job we should give it a name.

To access & dynamically create the cron job using SchedulerRegistry.

 const job = this.schedulerRegistry.getCronJob('notifications'); job.stop(); console.log(job.lastDate());
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We can also add a cron job dynamically.

addCronJob(name: string, seconds: string) { const job = new CronJob(`${seconds} * * * * *`, () => { this.logger.warn(`time (${seconds}) for job ${name} to run!`); }); this.schedulerRegistry.addCronJob(name, job); job.start(); this.logger.warn( `job ${name} added for each minute at ${seconds} seconds!`, ); }
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Cron Jobs can be both async and sync, Also they are used to run specific task at specific time.
If we want to run some task , Every X milliseconds like Polling, health checks, repeated tasks. Then we can use @Interval.

// similar to setInterval in nodejs @Interval(10000) // Every 10 seconds handleInterval() { console.log('Polling external service...'); }
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Also we have Timeout similar to setTimeout, they are used when we want to run a task once but after a delay.

  • Running a task once after app startup

  • Delaying execution of a retry or follow-up task

  • Debouncing logic (in rare backend scenarios)

@Timeout(5000) // After 5 seconds handleTimeout() { console.log('Initial sync task after startup delay'); }
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They both can be called dynamically using SchedulerRegistry.

if you have set Cron Job to run EVERY_10_MINUTE, then it will run in every multiple of 10.

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