toad-scheduler

In-memory TypeScript job scheduler that repeatedly executes given tasks within specified intervals of time (e. g. "each 20 seconds").

Node.js 12+ and modern browsers are supported

Getting started

First install the package:

npm i toad-scheduler

Next, set up your jobs:

const { ToadScheduler, SimpleIntervalJob, Task } = require('toad-scheduler')

const scheduler = new ToadScheduler()

const task = new Task('simple task', () => { counter++ })
const job = new SimpleIntervalJob({ seconds: 20, }, task)

scheduler.addSimpleIntervalJob(job)

// when stopping your app
scheduler.stop()

Usage with async tasks

In order to avoid unhandled rejections, make sure to use AsyncTask if your task is asynchronous:

const { ToadScheduler, SimpleIntervalJob, AsyncTask } = require('toad-scheduler')

const scheduler = new ToadScheduler()

const task = new AsyncTask(
    'simple task', 
    () => { return db.pollForSomeData().then((result) => { /* continue the promise chain */ }) },
    (err: Error) => { /* handle error here */ }
)
const job = new SimpleIntervalJob({ seconds: 20, }, task)

scheduler.addSimpleIntervalJob(job)

// when stopping your app
scheduler.stop()

Note that in order to avoid memory leaks, it is recommended to use promise chains instead of async/await inside task definition. See talk on common Promise mistakes for more details.

Asynchronous error handling

Note that your error handlers can be asynchronous and return a promise. In such case an additional catch block will be attached to them, and should there be an error while trying to resolve that promise, and logging error will be logged using the default error handler (console.error).

Preventing task run overruns

In case you want to prevent second instance of a task from being fired up while first one is still executing, you can use preventOverrun options:

import { ToadScheduler, SimpleIntervalJob, Task } from 'toad-scheduler';

const scheduler = new ToadScheduler();

const task = new Task('simple task', () => {
    // if this task runs long, second one won't be started until this one concludes
    console.log('Task triggered');
});

const job = new SimpleIntervalJob(
    { seconds: 20, runImmediately: true },
    task,
    { 
        id: 'id_1',
        preventOverrun: true,
    }
);

//create and start jobs
scheduler.addSimpleIntervalJob(job);

Using IDs and ES6-style imports

You can attach IDs to tasks to identify them later. This is helpful in projects that run a lot of tasks and especially if you want to target some of the tasks specifically (e. g. in order to stop or restart them, or to check their status).

import { ToadScheduler, SimpleIntervalJob, Task } from 'toad-scheduler';

const scheduler = new ToadScheduler();

const task = new Task('simple task', () => {
    console.log('Task triggered');
});

const job1 = new SimpleIntervalJob(
    { seconds: 20, runImmediately: true },
    task,
    { id: 'id_1' }
);

const job2 = new SimpleIntervalJob(
    { seconds: 15, runImmediately: true },
    task,
    { id: 'id_2' }
);

//create and start jobs
scheduler.addSimpleIntervalJob(job1);
scheduler.addSimpleIntervalJob(job2);

// stop job with ID: id_2
scheduler.stopById('id_2');

// remove job with ID: id_1
scheduler.removeById('id_1');

// check status of jobs
console.log(scheduler.getById('id_1').getStatus()); // returns Error (job not found)

console.log(scheduler.getById('id_2').getStatus()); // returns "stopped" and can be started again

Usage in clustered environments

toad-scheduler does not persist its state by design, and has no out-of-the-box concurrency management features. In case it is necessary to prevent parallel execution of jobs in clustered environment, it is highly recommended to use redis-semaphore in your tasks.

Here is an example:

import { randomUUID } from 'crypto'

import type Redis from 'ioredis'
import { Mutex } from 'redis-semaphore'
import type { LockOptions } from 'redis-semaphore'
import { AsyncTask } from 'toad-scheduler';

export type BackgroundJobConfiguration = {
    jobId: string
}

export type LockConfiguration = {
    lockName?: string
    refreshInterval?: number
    lockTimeout: number
}

export abstract class AbstractBackgroundJob {
    public readonly jobId: string
    protected readonly redis: Redis

    protected constructor(
        options: BackgroundJobConfiguration,
        redis: Redis,
    ) {
        this.jobId = options.jobId
        this.redis = redis
    }

    protected abstract processInternal(executionUuid: string): Promise<void>

    async process() {
        const uuid = randomUUID()

        try {
            await this.processInternal(uuid)
        } catch (err) {
            console.error(logObject)
        }
    }

    protected getJobMutex(key: string, options: LockOptions) {
        return new Mutex(this.redis, this.getJobLockName(key), options)
    }

    protected async tryAcquireExclusiveLock(lockConfiguration: LockConfiguration) {
        const mutex = this.getJobMutex(lockConfiguration.lockName ?? 'exclusive', {
            acquireAttemptsLimit: 1,
            refreshInterval: lockConfiguration.refreshInterval,
            lockTimeout: lockConfiguration.lockTimeout,
        })

        const lock = await mutex.tryAcquire()
        // If someone else already has this lock, skip
        if (!lock) {
            return
        }

        return mutex
    }

    protected getJobLockName(key: string) {
        return `${this.jobId}:locks:${key}`
    }
}

function createTask(job: AbstractBackgroundJob): AsyncTask {
    return new AsyncTask(
        job.jobId,
        () => {
            return job.process()
        },
    )
}

API for schedule

• days?: number - how many days to wait before executing the job for the next time;
• hours?: number - how many hours to wait before executing the job for the next time;
• minutes?: number - how many minutes to wait before executing the job for the next time;
• seconds?: number - how many seconds to wait before executing the job for the next time;
• milliseconds?: number - how many milliseconds to wait before executing the job for the next time;
• runImmediately?: boolean - if set to true, in addition to being executed on a given interval, job will also be executed immediately when added or restarted.

API for jobs

• start(): void - starts, or restarts (if it's already running) the job;
• stop(): void - stops the job. Can be restarted again with start command;
• getStatus(): JobStatus - returns the status of the job, which is one of: running, stopped.

API for scheduler

• addSimpleIntervalJob(job: SimpleIntervalJob): void - registers and starts a new job;
• addLongIntervalJob(job: SimpleIntervalJob): void - registers and starts a new job with support for intervals longer than 24.85 days;
• addIntervalJob(job: SimpleIntervalJob | LongIntervalJob): void - registers and starts new interval-based job;
• stop(): void - stops all jobs, registered in the scheduler;
• getById(id: string): Job - returns the job with a given id.
• existsById(id: string): boolean - returns true if job with given id exists, false otherwise.
• stopById(id: string): void - stops the job with a given id.
• removeById(id: string): Job | undefined - stops the job with a given id and removes it from the scheduler. If no such job exists, returns undefined, otherwise returns the job.
• startById(id: string): void - starts, or restarts (if it's already running) the job with a given id.