hr.length-of-service

export function lengthOfService(startDate: string, endDate: string): ServiceLength

/** Service as a person states it, plus the exact day count. */
export interface ServiceLength {
  /** completed years */
  readonly years: number;
  /** completed months after the years, 0-11 */
  readonly months: number;
  /** days after the months */
  readonly days: number;
  /** every day from startDate to endDate, both included */
  readonly totalDays: number;
}

import { lengthOfService } from "#fune/hr.length-of-service@^1";

import { addDays, daysBetween } from "./dates_add_days.ts";  ← from dates.add-days ^1.0.0 · built alongside by fune
import { addMonths } from "./dates_add_months.ts";  ← from dates.add-months ^1.0.0 · built alongside by fune
import { type ServiceLength } from "./hr_length_of_service_types.ts";

/**
 * Completed years, months and days of service, both end dates included.
 *
 * The end is moved to the following day so that a service period ending on
 * the eve of an anniversary counts as a whole year; forgetting that is the
 * off-by-one that denies someone a statutory right by a day.
 */
export function lengthOfService(startDate: string, endDate: string): ServiceLength {
  const totalDays = daysBetween(startDate, endDate) + 1;
  if (totalDays < 1) {
    throw new RangeError(`endDate ${endDate} is before startDate ${startDate}`);
  }
  const endExclusive = addDays(endDate, 1);
  let months =
    (Number(endExclusive.slice(0, 4)) - Number(startDate.slice(0, 4))) * 12 +
    (Number(endExclusive.slice(5, 7)) - Number(startDate.slice(5, 7)));
  while (months > 0 && addMonths(startDate, months) > endExclusive) months -= 1;
  const anniversary = addMonths(startDate, months);
  return {
    years: Math.floor(months / 12),
    months: months % 12,
    days: daysBetween(anniversary, endExclusive),
    totalDays,
  };
}

Install

fune build

With that line in your source, in a TypeScript project (language typescript in fune.project), fune build resolves it and its 2 dependencies, pins them in fune.lock, downloads only the TypeScript package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:

fune add hr.length-of-service

The manifest, vectors and README with only the TypeScript implementation. Install it without the registry with fune add ./hr.length-of-service-1.0.0-typescript.fune, or fetch it from a terminal with fune pull hr.length-of-service@1.0.0:typescript.

The whole function, every language, is one file too: hr.length-of-service-1.0.0.fune, 9,867 bytes, sha256 ffcde6ff77b8bcb654ea1aeb5ac3a10f4e19609b983b285e8bd386b8e4d1dc82. It installs into a project of any language.

// fune: before hr.length-of-service

// fune: after hr.length-of-service

// fune: replace dates.add-days in hr.length-of-service
// fune: replace dates.add-months in hr.length-of-service

// fune: step hr.length-of-service after <n|label>

More from the author

**Month ends.** A month is completed when the same day-of-month comes round again; a start on the 29th, 30th or 31st uses the last day of a shorter month instead (dates.add-months clamps: 31 January plus one month is 28 February). So 31 January to 27 February inclusive is one whole month: every day of February up to its 28th day is covered. Callers with a contractual rule for these starts should apply it themselves.

This does not decide whether service was continuous (breaks, TUPE transfers, strikes and the ERA 1996 Part XIV rules); it measures the period it is given.

Source: Employment Rights Act 1996 s.211, https://www.legislation.gov.uk/ukpga/1996/18/section/211.

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