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week_of_year.ts
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week_of_year.ts
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// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
import { DAY, WEEK } from "./constants.ts";
const DAYS_PER_WEEK = 7;
enum Day {
Sun,
Mon,
Tue,
Wed,
Thu,
Fri,
Sat,
}
/**
* Returns the ISO week number of the provided date (1-53).
*
* @example
* ```ts
* import { weekOfYear } from "https://deno.land/std@$STD_VERSION/datetime/week_of_year.ts";
*
* weekOfYear(new Date("2020-12-28T03:24:00")); // Returns 53
* ```
*
* @return Number of the week in year
*/
export function weekOfYear(date: Date): number {
const workingDate = new Date(
Date.UTC(date.getFullYear(), date.getMonth(), date.getDate()),
);
const day = workingDate.getUTCDay();
const nearestThursday = workingDate.getUTCDate() +
Day.Thu -
(day === Day.Sun ? DAYS_PER_WEEK : day);
workingDate.setUTCDate(nearestThursday);
// Get first day of year
const yearStart = new Date(Date.UTC(workingDate.getUTCFullYear(), 0, 1));
// return the calculated full weeks to nearest Thursday
return Math.ceil((workingDate.getTime() - yearStart.getTime() + DAY) / WEEK);
}