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diff --git a/date-fns/src/getWeek/index.ts b/date-fns/src/getWeek/index.ts
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+import startOfWeek from '../startOfWeek/index'
+import startOfWeekYear from '../startOfWeekYear/index'
+import toDate from '../toDate/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+import { LocaleOptions, WeekStartOptions, FirstWeekContainsDateOptions } from '../types'
+
+const MILLISECONDS_IN_WEEK = 604800000
+
+/**
+ * @name getWeek
+ * @category Week Helpers
+ * @summary Get the local week index of the given date.
+ *
+ * @description
+ * Get the local week index of the given date.
+ * The exact calculation depends on the values of
+ * `options.weekStartsOn` (which is the index of the first day of the week)
+ * and `options.firstWeekContainsDate` (which is the day of January, which is always in
+ * the first week of the week-numbering year)
+ *
+ * Week numbering: https://en.wikipedia.org/wiki/Week#Week_numbering
+ *
+ * ### v2.0.0 breaking changes:
+ *
+ * - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
+ *
+ * @param {Date|Number} date - the given date
+ * @param {Object} [options] - an object with options.
+ * @param {Locale} [options.locale=defaultLocale] - the locale object. See [Locale]{@link https://date-fns.org/docs/Locale}
+ * @param {0|1|2|3|4|5|6} [options.weekStartsOn=0] - the index of the first day of the week (0 - Sunday)
+ * @param {1|2|3|4|5|6|7} [options.firstWeekContainsDate=1] - the day of January, which is always in the first week of the year
+ * @returns {Number} the week
+ * @throws {TypeError} 1 argument required
+ * @throws {RangeError} `options.weekStartsOn` must be between 0 and 6
+ * @throws {RangeError} `options.firstWeekContainsDate` must be between 1 and 7
+ *
+ * @example
+ * // Which week of the local week numbering year is 2 January 2005 with default options?
+ * const result = getISOWeek(new Date(2005, 0, 2))
+ * //=> 2
+ *
+ * // Which week of the local week numbering year is 2 January 2005,
+ * // if Monday is the first day of the week,
+ * // and the first week of the year always contains 4 January?
+ * const result = getISOWeek(new Date(2005, 0, 2), {
+ *   weekStartsOn: 1,
+ *   firstWeekContainsDate: 4
+ * })
+ * //=> 53
+ */
+
+export default function getWeek(dirtyDate: Date | number, options?: LocaleOptions & WeekStartOptions & FirstWeekContainsDateOptions): number {
+  requiredArgs(1, arguments)
+
+  const date = toDate(dirtyDate)
+  const diff =
+    startOfWeek(date, options).getTime() -
+    startOfWeekYear(date, options).getTime()
+
+  // Round the number of days to the nearest integer
+  // because the number of milliseconds in a week is not constant
+  // (e.g. it's different in the week of the daylight saving time clock shift)
+  return Math.round(diff / MILLISECONDS_IN_WEEK) + 1
+}