Library for getting dates in the weeks around another date
このスクリプトは単体で利用できません。右のようなメタデータを含むスクリプトから、ライブラリとして読み込まれます: // @require https://update.greasyfork.org/scripts/559387/1718432/getRelativeWeekday.js
// ==UserScript==
// @name getRelativeWeekday
// @namespace https://github.com/nate-kean/
// @version 2025.12.21
// @description Library for getting dates in the weeks around another date
// @author Nate Kean
// @icon data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==
// @grant none
// @license MIT
// ==/UserScript==
// @ts-check
const Day = Object.freeze({
SUNDAY: 0,
MONDAY: 1,
TUESDAY: 2,
WEDNESDAY: 3,
THURSDAY: 4,
FRIDAY: 5,
SATURDAY: 6,
});
/**
* @typedef {typeof Day[keyof typeof Day]} DayT
*/
/**
* NEXT: The next occurrence (always in the future)
* LAST: The last occurrence (always in the past)
* THIS: The nearest occurrence in the current week (Mon-Sun)
*/
const DateDir = Object.freeze({
LAST: -1,
THIS: 0,
NEXT: 1,
});
/**
* @typedef {typeof DateDir[keyof typeof DateDir]} DateDirT
*/
/**
* Get a relative weekday from a target date.
*
* By Claude Sonnet 4.5:
* https://claude.ai/public/artifacts/d666c5fe-6e91-4186-a46f-ae4eb046636e
*
* Manually ported to JavaScript because I was using this for a Python project
* before
*
* @param {Date} targetDate Date to calculate from
* @param {DayT} weekday
* @param {DateDirT} direction
* @param {boolean} includeToday whether to include targetDate if it matches weekday
* @returns {Date}
*
* @example
* // returns Sun Jan 12 2025 00:00:00
* const target = new Date("01/15/2025"); // Wednesday
* getRelativeWeekday(target, DateDir.LAST, Day.SUNDAY);
* @example
* // returns Thu Jan 16 2025 00:00:00
* getRelativeWeekday(target, DateDir.THIS, Day.THURSDAY);
* @example
* // returns Thu Jan 23 2025 00:00:00
* getRelativeWeekday(target, DateDir.NEXT, Day.THURSDAY);
*/
function getRelativeWeekday(
targetDate,
direction,
weekday,
includeToday = false,
) {
const currentWeekday = targetDate.getDay();
const result = new Date(targetDate);
switch (direction) {
case DateDir.LAST: {
// Calculate days back to the target weekday
let daysForward = (currentWeekday - weekday) % 7; // Zero or negative
if (daysForward === 0 && !includeToday) {
// If this would make the result land on today, make it a week
// ago instead
daysForward = 7;
}
result.setDate(result.getDate() + daysForward);
return result;
}
case DateDir.THIS: {
// Find the date within the current week (Monday to Sunday)
// Current week starts on the Monday of targetDate's week
let daysForward = weekday - currentWeekday; // Zero or positive
if (daysForward === 0 && !includeToday) {
// If this would make the result land on today, make it a week
// from now instead
daysForward = 7;
}
result.setDate(result.getDate() + daysForward);
return result;
}
case DateDir.NEXT: {
// Calculate days forward to the target weekday
let daysForward = (weekday - currentWeekday) % 7; // Zero or positive
daysForward += 7;
result.setDate(result.getDate() + daysForward);
return result;
}
}
}