Advanced Format

The Advanced Format plugin provides utility methods for advanced date calculations including quarters, week numbers, ISO weeks, and day of year calculations.

Installation

import { fdu } from "@pyyupsk/fdu";
import { advancedFormat } from "@pyyupsk/fdu/plugins/advanced-format";

fdu.extend(advancedFormat);

Day Methods

dayOfYear()

Get the day number of the year (1-366).

Syntax

dayOfYear(): number

Returns

number - Day number (1 = Jan 1, 365/366 = Dec 31)

Examples

const date = fdu("2025-01-01");
date.dayOfYear(); // 1

const date2 = fdu("2025-10-05");
date2.dayOfYear(); // 278

const date3 = fdu("2025-12-31");
date3.dayOfYear(); // 365

isoWeekday()

Get ISO day of week where Monday = 1 and Sunday = 7.

Syntax

isoWeekday(): number

Returns

number - ISO day of week (1-7, Monday = 1, Sunday = 7)

Examples

const monday = fdu("2025-10-06");
monday.isoWeekday(); // 1

const sunday = fdu("2025-10-05");
sunday.isoWeekday(); // 7

Week Methods

weekOfYear()

Get the week number of the year (1-53). Uses ISO 8601 standard where week 1 is the first week with a Thursday.

Syntax

weekOfYear(): number

Returns

number - Week number of the year (1-53)

Examples

const date = fdu("2025-01-01");
date.weekOfYear(); // 1

const date2 = fdu("2025-10-05");
date2.weekOfYear(); // 40

isoWeek()

Get ISO week number of the year (1-53) using the ISO 8601 week date system.

Syntax

isoWeek(): number

Returns

number - ISO week number (1-53)

Examples

const date = fdu("2025-10-05");
date.isoWeek(); // 40

Year Methods

weekYear()

Get the year that the week belongs to. This can differ from the calendar year for dates in early January or late December.

Syntax

weekYear(): number

Returns

number - Week year

Examples

// Week 1 of 2025 might start in December 2024
const date1 = fdu("2024-12-30");
date1.weekYear(); // 2025 (if it's part of week 1 of 2025)

const date2 = fdu("2025-01-05");
date2.weekYear(); // 2025

isoWeekYear()

Get ISO week-numbering year according to ISO 8601.

Syntax

isoWeekYear(): number

Returns

number - ISO week year

Examples

const date = fdu("2025-01-01");
date.isoWeekYear(); // 2025

isoWeeksInYear()

Get the number of ISO weeks in the year (52 or 53).

Syntax

isoWeeksInYear(): number

Returns

number - Number of ISO weeks in year (52 or 53)

Examples

const date2025 = fdu("2025-01-01");
date2025.isoWeeksInYear(); // 52

const date2020 = fdu("2020-01-01");
date2020.isoWeeksInYear(); // 53

Quarter Methods

quarter()

Get the quarter of the year (1-4).

Syntax

quarter(): number

Returns

number - Quarter number (1 = Q1, 2 = Q2, 3 = Q3, 4 = Q4)

Examples

const q1 = fdu("2025-02-15");
q1.quarter(); // 1

const q2 = fdu("2025-05-20");
q2.quarter(); // 2

const q3 = fdu("2025-08-10");
q3.quarter(); // 3

const q4 = fdu("2025-10-05");
q4.quarter(); // 4

Complete Example

import { fdu } from "@pyyupsk/fdu";
import { advancedFormat } from "@pyyupsk/fdu/plugins/advanced-format";

// Register the plugin
fdu.extend(advancedFormat);

const date = fdu("2025-10-05");

// Day calculations
console.log(`Day of year: ${date.dayOfYear()}`); // Day of year: 278
console.log(`ISO weekday: ${date.isoWeekday()}`); // ISO weekday: 7

// Week calculations
console.log(`Week of year: ${date.weekOfYear()}`); // Week of year: 40
console.log(`ISO week: ${date.isoWeek()}`); // ISO week: 40

// Year calculations
console.log(`Week year: ${date.weekYear()}`); // Week year: 2025
console.log(`ISO week year: ${date.isoWeekYear()}`); // ISO week year: 2025
console.log(`ISO weeks in year: ${date.isoWeeksInYear()}`); // ISO weeks in year: 52

// Quarter
console.log(`Quarter: Q${date.quarter()}`); // Quarter: Q4

Use Cases

Calendar Applications

import { fdu } from "@pyyupsk/fdu";
import { advancedFormat } from "@pyyupsk/fdu/plugins/advanced-format";

fdu.extend(advancedFormat);

// Display ISO week number in calendar
const today = fdu();
console.log(`Week ${today.isoWeek()} of ${today.isoWeekYear()}`);
// "Week 40 of 2025"

// Show day of year progress
const dayOfYear = today.dayOfYear();
const totalDays = fdu(`${today.year()}-12-31`).dayOfYear();
const progress = ((dayOfYear / totalDays) * 100).toFixed(1);
console.log(`${progress}% of the year complete`);
// "76.7% of the year complete"

Financial Reporting

import { fdu } from "@pyyupsk/fdu";
import { advancedFormat } from "@pyyupsk/fdu/plugins/advanced-format";

fdu.extend(advancedFormat);

// Get current quarter for financial reports
const today = fdu();
const currentQuarter = today.quarter();
console.log(`Q${currentQuarter} ${today.year()} Report`);
// "Q4 2025 Report"

// Check if date is in fiscal year
function getFiscalYear(date: typeof today) {
  const quarter = date.quarter();
  return quarter === 1 ? date.year() : date.year() + 1;
}

Week-based Planning

import { fdu } from "@pyyupsk/fdu";
import { advancedFormat } from "@pyyupsk/fdu/plugins/advanced-format";

fdu.extend(advancedFormat);

// Plan by ISO week
const project = fdu("2025-10-05");
console.log(`Week ${project.isoWeek()}: Start project planning`);
// "Week 40: Start project planning"

// Check if date is a weekday (Monday-Friday)
const date = fdu();
const isoDay = date.isoWeekday();
const isWeekday = isoDay >= 1 && isoDay <= 5;
console.log(isWeekday ? "Weekday" : "Weekend");

API Reference

All methods are added to the FduInstance interface and are available after registering the plugin:

Method	Return Type	Description
`dayOfYear()`	`number`	Day number of the year (1-366)
`isoWeekday()`	`number`	ISO day of week (1-7, Monday=1, Sunday=7)
`weekOfYear()`	`number`	Week number of the year (1-53)
`isoWeek()`	`number`	ISO week number (1-53)
`weekYear()`	`number`	Year that the week belongs to
`isoWeekYear()`	`number`	ISO week-numbering year
`isoWeeksInYear()`	`number`	Number of ISO weeks in year (52 or 53)
`quarter()`	`number`	Quarter of the year (1-4)

Plugin methods are only available after the plugin has been registered with fdu.extend(). Attempting to use them before registration will result in an error.

Advanced Format

On this page