Task Scheduling ​

Task scheduling allows you to schedule arbitrary code (methods/functions) to execute at a fixed date/time, at recurring intervals, or once after a specified interval. In the Linux world, this is often handled by packages like cron at the OS level. For Deno apps, we have a native module (yet in unstable) called Deno.cron, to provide cron-like functionality

References:

• https://deno.land/api@v1.40.5?s=Deno.cron
• https://examples.deno.land/cron
• https://docs.nestjs.com/techniques/task-scheduling

Installation ​

No need to install an extra module, you can import it from danet/mod.ts

To activate job scheduling, import the ScheduleModule into the root AppModule:

@@filename(app.module)
import { ScheduleModule, Module } from 'danet/mod.ts';

@Module({
  imports: [ScheduleModule],
})
export class AppModule {}

Registration occurs when the onAppBootstrap lifecycle hook occurs, ensuring that all modules have loaded and declared any scheduled jobs.

Declarative cron jobs ​

A cron job schedules an arbitrary function (method call) to run automatically. Cron jobs can run:

• Once, at a specified date/time.
• On a recurring basis; recurring jobs can run at a specified instant within a specified interval (for example, once per hour, once per week, once every 5 minutes)

Declare a cron job with the @Cron() decorator preceding the method definition containing the code to be executed, as follows:

import { Cron, Injectable } from 'danet/mod.ts';

@Injectable()
export class TasksService {
  private readonly logger = new Logger(TasksService.name);

  @Cron('45 * * * *')
  handleCron() {
    this.logger.debug('Called when the current minutes is 45');
  }
}

In this example, the handleCron() method will be called each time the current minutes is 45. In other words, the method will be run once per minute, at the 45 minute mark.

The @Cron() decorator supports all standard cron patterns:

• Asterisk (e.g. *)
• Ranges (e.g. 1-3,5)
• Steps (e.g. */2)

In the example above, we passed 45 * * * * * to the decorator. The following key shows how each position in the cron pattern string is interpreted:

* * * * *
| | | | |
| | | | day of week
| | | months
| | day of month
| hours
minutes

Some sample cron patterns are:

Like @nestjs/schedule package, we also provides a convenient enum with commonly used cron patterns. You can use this enum as follows:

import { Injectable, Logger, Cron, CronExpression  } from 'danet/mod.ts';

@Injectable()
export class TasksService {
  private readonly logger = new Logger(TasksService.name);

  @Cron(CronExpression.EVERY_30_MINUTES)
  handleCron() {
    this.logger.debug('Called every 30 minutes');
  }
}

In this example, the handleCron() method will be called every 30 minutes.

Declarative intervals ​

To declare that a method should run at a (recurring) specified interval, prefix the method definition with the @Interval() decorator. Pass the interval value, as a number in milliseconds, to the decorator as shown below:

@Interval(10000)
handleInterval() {
  this.logger.debug('Called every 10 seconds');
}

info Hint This mechanism uses the JavaScript setInterval() function under the hood. You can also utilize a cron job to schedule recurring jobs.

Declarative timeouts ​

To declare that a method should run (once) at a specified timeout, prefix the method definition with the @Timeout() decorator. Pass the relative time offset (in milliseconds), from application startup, to the decorator as shown below:

@Timeout(5000)
handleTimeout() {
  this.logger.debug('Called once after 5 seconds');
}

info Hint This mechanism uses the JavaScript setTimeout() function under the hood.

Dynamic schedule module API ​

Warning 🚧 this module does not support dynamic scheduling yet.

Example ​

A working example is available here.