5 files changed, 148 insertions, 0 deletions
diff --git a/date-fns/src/endOfDecade/benchmark.js b/date-fns/src/endOfDecade/benchmark.js
new file mode 100644
index 0000000..43296e1
--- /dev/null
+++ b/date-fns/src/endOfDecade/benchmark.js
@@ -0,0 +1,15 @@
+// @flow
+/* eslint-env mocha */
+/* global suite, benchmark */
+
+import endOfDecade from '.'
+
+suite('endOfDecade', function () {
+  benchmark('date-fns', function () {
+    return endOfDecade(this.date)
+  })
+}, {
+  setup: function () {
+    this.date = new Date()
+  }
+})
diff --git a/date-fns/src/endOfDecade/index.d.ts b/date-fns/src/endOfDecade/index.d.ts
new file mode 100644
index 0000000..c723f13
--- /dev/null
+++ b/date-fns/src/endOfDecade/index.d.ts
@@ -0,0 +1,4 @@
+// This file is generated automatically by `scripts/build/typings.js`. Please, don't change it.
+
+import { endOfDecade } from 'date-fns'
+export default endOfDecade
diff --git a/date-fns/src/endOfDecade/index.js.flow b/date-fns/src/endOfDecade/index.js.flow
new file mode 100644
index 0000000..364a3bb
--- /dev/null
+++ b/date-fns/src/endOfDecade/index.js.flow
@@ -0,0 +1,57 @@
+// @flow
+// This file is generated automatically by `scripts/build/typings.js`. Please, don't change it.
+
+export type Interval = {
+  start: Date | number,
+  end: Date | number,
+}
+
+export type Locale = {
+  code?: string,
+  formatDistance?: (...args: Array<any>) => any,
+  formatRelative?: (...args: Array<any>) => any,
+  localize?: {
+    ordinalNumber: (...args: Array<any>) => any,
+    era: (...args: Array<any>) => any,
+    quarter: (...args: Array<any>) => any,
+    month: (...args: Array<any>) => any,
+    day: (...args: Array<any>) => any,
+    dayPeriod: (...args: Array<any>) => any,
+  },
+  formatLong?: {
+    date: (...args: Array<any>) => any,
+    time: (...args: Array<any>) => any,
+    dateTime: (...args: Array<any>) => any,
+  },
+  match?: {
+    ordinalNumber: (...args: Array<any>) => any,
+    era: (...args: Array<any>) => any,
+    quarter: (...args: Array<any>) => any,
+    month: (...args: Array<any>) => any,
+    day: (...args: Array<any>) => any,
+    dayPeriod: (...args: Array<any>) => any,
+  },
+  options?: {
+    weekStartsOn?: 0 | 1 | 2 | 3 | 4 | 5 | 6,
+    firstWeekContainsDate?: 1 | 2 | 3 | 4 | 5 | 6 | 7,
+  },
+}
+
+export type Duration = {
+  years?: number,
+  months?: number,
+  weeks?: number,
+  days?: number,
+  hours?: number,
+  minutes?: number,
+  seconds?: number,
+}
+
+export type Day = 0 | 1 | 2 | 3 | 4 | 5 | 6
+
+declare module.exports: (
+  date: Date | number,
+  options?: {
+    additionalDigits?: 0 | 1 | 2,
+  }
+) => Date
diff --git a/date-fns/src/endOfDecade/index.ts b/date-fns/src/endOfDecade/index.ts
new file mode 100644
index 0000000..11c5ddb
--- /dev/null
+++ b/date-fns/src/endOfDecade/index.ts
@@ -0,0 +1,37 @@
+import toDate from '../toDate/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+
+/**
+ * @name endOfDecade
+ * @category Decade Helpers
+ * @summary Return the end of a decade for the given date.
+ *
+ * @description
+ * Return the end of a decade for the given date.
+ *
+ * ### 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 original date
+ * @returns {Date} the end of a decade
+ * @param {Object} [options] - an object with options.
+ * @param {0|1|2} [options.additionalDigits=2] - passed to `toDate`. See [toDate]{@link https://date-fns.org/docs/toDate}
+ * @throws {TypeError} 1 argument required
+ * @throws {RangeError} `options.additionalDigits` must be 0, 1 or 2
+ *
+ * @example
+ * // The end of a decade for 12 May 1984 00:00:00:
+ * const result = endOfDecade(new Date(1984, 4, 12, 00, 00, 00))
+ * //=> Dec 31 1989 23:59:59.999
+ */
+export default function endOfDecade(dirtyDate: Date | number): Date {
+  requiredArgs(1, arguments)
+
+  const date = toDate(dirtyDate)
+  const year = date.getFullYear()
+  const decade = 9 + Math.floor(year / 10) * 10
+  date.setFullYear(decade, 11, 31)
+  date.setHours(23, 59, 59, 999)
+  return date
+}
diff --git a/date-fns/src/endOfDecade/test.ts b/date-fns/src/endOfDecade/test.ts
new file mode 100644
index 0000000..6328154
--- /dev/null
+++ b/date-fns/src/endOfDecade/test.ts
@@ -0,0 +1,35 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'power-assert'
+import endOfDecade from '.'
+
+describe('endOfDecade', function() {
+  it('returns the date with the time set to 23:59:59.999 and the date set to the last millisecond of a decade', function() {
+    const date = new Date(2017, 3 /* Apr */, 10, 0, 0, 0)
+    const result = endOfDecade(date)
+    assert.deepEqual(result, new Date(2019, 11 /* Dec */, 31, 23, 59, 59, 999))
+  })
+
+  it('accepts a timestamp', function() {
+    const date = new Date(2007, 9 /* Oct */, 10, 0, 0, 0).getTime()
+    const result = endOfDecade(date)
+    assert.deepEqual(result, new Date(2009, 11 /* Dec */, 31, 23, 59, 59, 999))
+  })
+
+  it('does not mutate the original date', function() {
+    const date = new Date(2038, 0 /* Jan */, 19, 3, 14, 8)
+    endOfDecade(date)
+    assert.deepEqual(date, new Date(2038, 0 /* Jan */, 19, 3, 14, 8))
+  })
+
+  it('returns `Invalid Date` if the given date is invalid', function() {
+    const result = endOfDecade(new Date(NaN))
+    //@ts-expect-error
+    assert(result instanceof Date && isNaN(result))
+  })
+
+  it('throws TypeError exception if passed less than 1 argument', function() {
+    assert.throws(endOfDecade.bind(null), TypeError)
+  })
+})