5 files changed, 178 insertions, 0 deletions
diff --git a/date-fns/src/subMonths/benchmark.js b/date-fns/src/subMonths/benchmark.js
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+++ b/date-fns/src/subMonths/benchmark.js
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+// @flow
+/* eslint-env mocha */
+/* global suite, benchmark */
+
+import subMonths from '.'
+import moment from 'moment'
+
+suite('subMonths', function () {
+  benchmark('date-fns', function () {
+    return subMonths(this.date, 7)
+  })
+
+  benchmark('Moment.js', function () {
+    return this.moment.subtract(7, 'months')
+  })
+}, {
+  setup: function () {
+    this.date = new Date()
+    this.moment = moment()
+  }
+})
diff --git a/date-fns/src/subMonths/index.d.ts b/date-fns/src/subMonths/index.d.ts
new file mode 100644
index 0000000..dd963a1
--- /dev/null
+++ b/date-fns/src/subMonths/index.d.ts
@@ -0,0 +1,4 @@
+// This file is generated automatically by `scripts/build/typings.js`. Please, don't change it.
+
+import { subMonths } from 'date-fns'
+export default subMonths
diff --git a/date-fns/src/subMonths/index.js.flow b/date-fns/src/subMonths/index.js.flow
new file mode 100644
index 0000000..f568f0d
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+++ b/date-fns/src/subMonths/index.js.flow
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+// @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, amount: number) => Date
diff --git a/date-fns/src/subMonths/index.ts b/date-fns/src/subMonths/index.ts
new file mode 100644
index 0000000..d827fad
--- /dev/null
+++ b/date-fns/src/subMonths/index.ts
@@ -0,0 +1,32 @@
+import toInteger from '../_lib/toInteger/index'
+import addMonths from '../addMonths/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+
+/**
+ * @name subMonths
+ * @category Month Helpers
+ * @summary Subtract the specified number of months from the given date.
+ *
+ * @description
+ * Subtract the specified number of months from 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 date to be changed
+ * @param {Number} amount - the amount of months to be subtracted. Positive decimals will be rounded using `Math.floor`, decimals less than zero will be rounded using `Math.ceil`.
+ * @returns {Date} the new date with the months subtracted
+ * @throws {TypeError} 2 arguments required
+ *
+ * @example
+ * // Subtract 5 months from 1 February 2015:
+ * const result = subMonths(new Date(2015, 1, 1), 5)
+ * //=> Mon Sep 01 2014 00:00:00
+ */
+export default function subMonths(dirtyDate: Date | number, dirtyAmount: number): Date {
+  requiredArgs(2, arguments)
+
+  const amount = toInteger(dirtyAmount)
+  return addMonths(dirtyDate, -amount)
+}
diff --git a/date-fns/src/subMonths/test.ts b/date-fns/src/subMonths/test.ts
new file mode 100644
index 0000000..0b5c32d
--- /dev/null
+++ b/date-fns/src/subMonths/test.ts
@@ -0,0 +1,69 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'power-assert'
+import subMonths from '.'
+
+describe('subMonths', function() {
+  it('subtracts the given number of months', function() {
+    const result = subMonths(new Date(2015, 1 /* Feb */, 1), 5)
+    assert.deepEqual(result, new Date(2014, 8 /* Sep */, 1))
+  })
+
+  it('accepts a timestamp', function() {
+    const result = subMonths(new Date(2015, 8 /* Sep */, 1).getTime(), 12)
+    assert.deepEqual(result, new Date(2014, 8 /* Sep */, 1))
+  })
+
+  it('converts a fractional number to an integer', function() {
+    const result = subMonths(new Date(2015, 1 /* Feb */, 1), 5.999)
+    assert.deepEqual(result, new Date(2014, 8 /* Sep */, 1))
+  })
+
+  it('implicitly converts number arguments', function() {
+    // $ExpectedMistake
+    // @ts-expect-error
+    const result = subMonths(new Date(2015, 1 /* Feb */, 1), '5')
+    assert.deepEqual(result, new Date(2014, 8 /* Sep */, 1))
+  })
+
+  it('does not mutate the original date', function() {
+    const date = new Date(2014, 8 /* Sep */, 1)
+    subMonths(date, 12)
+    assert.deepEqual(date, new Date(2014, 8 /* Sep */, 1))
+  })
+
+  it('works well if the desired month has fewer days and the provided date is in the last day of a month', function() {
+    const date = new Date(2014, 11 /* Dec */, 31)
+    const result = subMonths(date, 3)
+    assert.deepEqual(result, new Date(2014, 8 /* Sep */, 30))
+  })
+
+  it('handles dates before 100 AD', function() {
+    const initialDate = new Date(0)
+    initialDate.setFullYear(1, 2 /* Mar */, 31)
+    initialDate.setHours(0, 0, 0, 0)
+    const expectedResult = new Date(0)
+    expectedResult.setFullYear(1, 1 /* Feb */, 28)
+    expectedResult.setHours(0, 0, 0, 0)
+    const result = subMonths(initialDate, 1)
+    assert.deepEqual(result, expectedResult)
+  })
+
+  it('returns `Invalid Date` if the given date is invalid', function() {
+    const result = subMonths(new Date(NaN), 5)
+    // @ts-expect-error
+    assert(result instanceof Date && isNaN(result))
+  })
+
+  it('returns `Invalid Date` if the given amount is NaN', function() {
+    const result = subMonths(new Date(2015, 1 /* Feb */, 1), NaN)
+    // @ts-expect-error
+    assert(result instanceof Date && isNaN(result))
+  })
+
+  it('throws TypeError exception if passed less than 2 arguments', function() {
+    assert.throws(subMonths.bind(null), TypeError)
+    assert.throws(subMonths.bind(null, 1), TypeError)
+  })
+})