@philiprehberger/cron-kit

v0.3.5

Published

a day ago

Cron job scheduler with overlap prevention, timezones, and job management

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@philiprehberger/cron-kit

Cron job scheduler with overlap prevention, timezones, and job management

Installation

npm install @philiprehberger/cron-kit

Usage

Basic

import { createScheduler } from '@philiprehberger/cron-kit';

const scheduler = createScheduler();

scheduler.addJob({
  name: 'cleanup',
  schedule: '0 3 * * *', // daily at 3am
  handler: async () => {
    await db.sessions.deleteExpired();
  },
});

scheduler.start();

With Options

scheduler.addJob({
  name: 'report',
  schedule: '0 9 * * 1', // every Monday at 9am
  timezone: 'Europe/Vienna',
  allowOverlap: false,    // skip if previous run still active
  handler: async () => { /* ... */ },
  onStart: () => console.log('Report started'),
  onComplete: (duration) => console.log(`Done in ${duration}ms`),
  onError: (err) => console.error('Report failed:', err),
  onOverlap: () => console.warn('Skipped — still running'),
});

Cron Expressions

Standard 5-field format: minute hour day-of-month month day-of-week

*     *     *     *     *
│     │     │     │     └── Day of week (0–6, Sun=0)
│     │     │     └──────── Month (1–12)
│     │     └────────────── Day of month (1–31)
│     └──────────────────── Hour (0–23)
└────────────────────────── Minute (0–59)

Supports: *, values (5), ranges (1-5), steps (*/5), lists (1,3,5)

When both day-of-month and day-of-week are specified (not *), the job runs when either field matches (OR logic), following standard cron behavior.

Preview Next Runs

import { nextRuns } from '@philiprehberger/cron-kit';

nextRuns('0 9 * * 1', 3);
// [Date, Date, Date] — next 3 Mondays at 9am

// Or from a job
scheduler.getJob('cleanup').nextRuns(5);

Job Management

scheduler.getJob('cleanup');   // job info
scheduler.getJobs();           // all jobs
scheduler.removeJob('cleanup');

// Update a job's schedule, handler, or other options
scheduler.updateJob('cleanup', {
  schedule: '0 4 * * *',      // change to 4am
  handler: async () => { /* new logic */ },
});

Job Info

const job = scheduler.getJob('cleanup');
job.name;         // 'cleanup'
job.running;      // boolean
job.lastRunAt;    // Date | null
job.lastDuration; // number | null (ms)
job.lastError;    // Error | null
job.runCount;     // number

Graceful Shutdown

scheduler.stop();               // stop scheduling (active jobs keep running)
await scheduler.shutdown();     // stop + wait for active jobs to finish

API

`createScheduler(): Scheduler`

Creates a new scheduler instance.

| Method | Signature | Description | |--------|-----------|-------------| | addJob | (config: JobConfig) => void | Register a job. Throws if name already exists. | | updateJob | (name: string, updates: Partial<Omit<JobConfig, 'name'>>) => void | Update a job's config. Re-parses schedule if changed. Throws if not found. | | removeJob | (name: string) => void | Remove a job by name. Throws if not found. | | getJob | (name: string) => JobInfo | Get info for a single job. Throws if not found. | | getJobs | () => JobInfo[] | Get info for all registered jobs. | | start | () => void | Start the scheduler tick loop. | | stop | () => void | Stop scheduling (active jobs keep running). | | shutdown | () => Promise<void> | Stop and wait for all active jobs to finish. |

`JobConfig`

| Property | Type | Required | Description | |----------|------|----------|-------------| | name | string | Yes | Unique job identifier. | | schedule | string | Yes | Cron expression (5 fields). | | handler | () => Promise<void> \| void | Yes | Function to execute. | | timezone | string | No | IANA timezone (e.g. "America/Denver"). | | allowOverlap | boolean | No | Skip execution if previous run is still active. Default: true. | | onStart | () => void | No | Called when job execution begins. | | onComplete | (duration: number) => void | No | Called on success with duration in ms. | | onError | (error: Error) => void | No | Called when handler throws. | | onOverlap | () => void | No | Called when execution is skipped due to overlap. |

`JobInfo`

| Property | Type | Description | |----------|------|-------------| | name | string | Job name. | | schedule | string | Cron expression. | | timezone | string \| undefined | Configured timezone. | | running | boolean | Whether the job is currently executing. | | lastRunAt | Date \| null | When the job last completed. | | lastDuration | number \| null | Last run duration in ms. | | lastError | Error \| null | Last error thrown by handler. | | runCount | number | Total completed executions. | | nextRuns | (count?: number) => Date[] | Preview upcoming run times. |

`nextRuns(expression: string, count?: number, timezone?: string): Date[]`

Returns an array of upcoming dates matching the cron expression.

`parseCronExpression(expression: string): ParsedCron`

Parses a 5-field cron expression into a structured object.

`matchesCron(cron: ParsedCron, date: Date): boolean`

Tests whether a date matches a parsed cron expression.

Limitations

Minute-level precision: The scheduler ticks every 30 seconds to check for matching jobs. All scheduling has minute-level granularity — second-level precision is not supported.
Timezone handling: Timezone conversion uses Date.toLocaleString() internally, which may have subtle differences across runtimes.
In-memory only: Job state is not persisted. Restarting the process resets all job counters and history.