# Quickstart: JavaScript

URL: https://workclock.karthik.nz/docs/quickstart/javascript.md

By the end of this page you will have a JavaScript program for Node.js that works out when a support ticket is due, counting only working hours, and how much of its SLA has been used.

## Install

workclock needs Node.js 22 or later. In your project's directory:

```sh
npm i workclock
```

The package ships its TypeScript types. In a browser, load it through a bundler, or without one from `workclock/web` ([Install: Browsers without a bundler](https://workclock.karthik.nz/docs/install.md#browsers-without-a-bundler)).

## Write the program

A support desk in London works 09:00–17:00 on weekdays with a lunch hour, and is closed on 25 and 28 December 2026. A ticket opened at 16:30 on Christmas Eve with an 8-hour SLA is due at 09:30 on 30 December. At 11:00 on 29 December, 2 hours 30 minutes of the SLA have been used.

In JavaScript, save this as `sla.mjs`. Instants are `Date`s or ISO 8601 strings with an offset, and durations are milliseconds. London time is UTC in December, so 16:30 London time is `"2026-12-24T16:30:00Z"`.

```js title="sla.mjs"
import { Schedule } from "workclock";

const HOUR = 3_600_000; // milliseconds

const support = new Schedule({
  timeZone: "Europe/London",
  rules: [
    { type: "workday", start: "09:00", end: "17:00" },
    { type: "break", start: "12:00", end: "13:00" },
    { type: "holidays", dates: ["2026-12-25", "2026-12-28"] },
  ],
});

const opened = "2026-12-24T16:30:00Z";
const due = support.add(opened, 8 * HOUR); // Date 2026-12-30T09:30:00.000Z
const now = "2026-12-29T11:00:00Z";
const used = support.between(opened, now); // 9000000 ms

console.log(`due ${due.toISOString()}, used ${used / HOUR} h`);
```

## Run it

```sh
node sla.mjs
```

It prints:

```text
due 2026-12-30T09:30:00.000Z, used 2.5 h
```

09:30 UTC is 09:30 London time in December:



## What just happened

`new Schedule` combined three rules, read in the `Europe/London` time zone: a `"workday"` rule for 09:00–17:00, which defaults to Monday to Friday, a `"break"` rule for 12:00–13:00, and a `"holidays"` rule for 25 and 28 December. `support.add` counted 8 hours of working time from the moment the ticket was opened, skipping the evening, the weekend, the holidays and the lunch hour, and returned the due instant as a `Date`. `support.between` returned the working time between two instants as a number of milliseconds, 9,000,000 here. [`js/examples/sla.mjs`](https://github.com/Karthik-beta/workclock/blob/main/js/examples/sla.mjs) extends this program with `nextPeriod`, which finds when the current stretch of working time ends, and `addMany`, which computes many due times in one call.

## Next steps

- [Schedules](https://workclock.karthik.nz/docs/concepts/schedules.md): how rules combine into working time.
- [Adding time](https://workclock.karthik.nz/docs/concepts/adding-time.md): what `add` and `sub` return, including at the edges of working time.