5 files changed, 253 insertions, 0 deletions
diff --git a/date-fns/src/differenceInISOWeekYears/benchmark.js b/date-fns/src/differenceInISOWeekYears/benchmark.js
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--- /dev/null
+++ b/date-fns/src/differenceInISOWeekYears/benchmark.js
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+// @flow
+/* eslint-env mocha */
+/* global suite, benchmark */
+
+import differenceInISOWeekYears from '.'
+
+suite('differenceInISOWeekYears', function () {
+  benchmark('date-fns', function () {
+    return differenceInISOWeekYears(this.dateA, this.dateB)
+  })
+}, {
+  setup: function () {
+    this.dateA = new Date()
+    this.dateB = new Date(this.dateA.getTime() + 604800000)
+  }
+})
diff --git a/date-fns/src/differenceInISOWeekYears/index.d.ts b/date-fns/src/differenceInISOWeekYears/index.d.ts
new file mode 100644
index 0000000..ce7cb57
--- /dev/null
+++ b/date-fns/src/differenceInISOWeekYears/index.d.ts
@@ -0,0 +1,4 @@
+// This file is generated automatically by `scripts/build/typings.js`. Please, don't change it.
+
+import { differenceInISOWeekYears } from 'date-fns'
+export default differenceInISOWeekYears
diff --git a/date-fns/src/differenceInISOWeekYears/index.js.flow b/date-fns/src/differenceInISOWeekYears/index.js.flow
new file mode 100644
index 0000000..c799819
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+++ b/date-fns/src/differenceInISOWeekYears/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: (
+  dateLeft: Date | number,
+  dateRight: Date | number
+) => number
diff --git a/date-fns/src/differenceInISOWeekYears/index.ts b/date-fns/src/differenceInISOWeekYears/index.ts
new file mode 100644
index 0000000..75f268c
--- /dev/null
+++ b/date-fns/src/differenceInISOWeekYears/index.ts
@@ -0,0 +1,63 @@
+import toDate from '../toDate/index'
+import differenceInCalendarISOWeekYears from '../differenceInCalendarISOWeekYears/index'
+import compareAsc from '../compareAsc/index'
+import subISOWeekYears from '../subISOWeekYears/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+
+/**
+ * @name differenceInISOWeekYears
+ * @category ISO Week-Numbering Year Helpers
+ * @summary Get the number of full ISO week-numbering years between the given dates.
+ *
+ * @description
+ * Get the number of full ISO week-numbering years between the given dates.
+ *
+ * ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_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).
+ *
+ * - The function was renamed from `differenceInISOYears` to `differenceInISOWeekYears`.
+ *   "ISO week year" is short for [ISO week-numbering year](https://en.wikipedia.org/wiki/ISO_week_date).
+ *   This change makes the name consistent with
+ *   locale-dependent week-numbering year helpers, e.g., `addWeekYears`.
+ *
+ * @param {Date|Number} dateLeft - the later date
+ * @param {Date|Number} dateRight - the earlier date
+ * @returns {Number} the number of full ISO week-numbering years
+ * @throws {TypeError} 2 arguments required
+ *
+ * @example
+ * // How many full ISO week-numbering years are between 1 January 2010 and 1 January 2012?
+ * var result = differenceInISOWeekYears(
+ *   new Date(2012, 0, 1),
+ *   new Date(2010, 0, 1)
+ * )
+ * //=> 1
+ */
+export default function differenceInISOWeekYears(
+  dirtyDateLeft: Date | number,
+  dirtyDateRight: Date | number
+): number {
+  requiredArgs(2, arguments)
+
+  let dateLeft = toDate(dirtyDateLeft)
+  const dateRight = toDate(dirtyDateRight)
+
+  const sign = compareAsc(dateLeft, dateRight)
+  const difference = Math.abs(
+    differenceInCalendarISOWeekYears(dateLeft, dateRight)
+  )
+  dateLeft = subISOWeekYears(dateLeft, sign * difference)
+
+  // Math.abs(diff in full ISO years - diff in calendar ISO years) === 1
+  // if last calendar ISO year is not full
+  // If so, result must be decreased by 1 in absolute value
+  const isLastISOWeekYearNotFull = Number(
+    compareAsc(dateLeft, dateRight) === -sign
+  )
+  const result = sign * (difference - isLastISOWeekYearNotFull)
+  // Prevent negative zero
+  return result === 0 ? 0 : result
+}
diff --git a/date-fns/src/differenceInISOWeekYears/test.ts b/date-fns/src/differenceInISOWeekYears/test.ts
new file mode 100644
index 0000000..f4192ee
--- /dev/null
+++ b/date-fns/src/differenceInISOWeekYears/test.ts
@@ -0,0 +1,115 @@
+/* eslint-env mocha */
+
+import assert from 'power-assert'
+import differenceInISOWeekYears from '.'
+
+describe('differenceInISOWeekYears', function () {
+  it('returns the number of full ISO week-numbering years between the given dates', function () {
+    const result = differenceInISOWeekYears(
+      new Date(2012, 6 /* Jul */, 2, 18, 0),
+      new Date(2011, 6 /* Jul */, 2, 6, 0)
+    )
+    assert(result === 1)
+  })
+
+  it('returns a negative number if the time value of the first date is smaller', function () {
+    const result = differenceInISOWeekYears(
+      new Date(2011, 6 /* Jul */, 2, 6, 0),
+      new Date(2012, 6 /* Jul */, 2, 18, 0)
+    )
+    assert(result === -1)
+  })
+
+  it('accepts timestamps', function () {
+    const result = differenceInISOWeekYears(
+      new Date(2014, 6 /* Jul */, 2).getTime(),
+      new Date(2010, 6 /* Jul */, 2).getTime()
+    )
+    assert(result === 4)
+  })
+
+  it('handles dates before 100 AD', function () {
+    const firstDate = new Date(0)
+    firstDate.setFullYear(14, 0 /* Jan */, 1)
+    firstDate.setHours(0, 0, 0, 0)
+    const secondDate = new Date(0)
+    secondDate.setFullYear(0, 0 /* Jan */, 1)
+    secondDate.setHours(0, 0, 0, 0)
+    const result = differenceInISOWeekYears(firstDate, secondDate)
+    assert(result === 14)
+  })
+
+  describe('edge cases', function () {
+    it('the difference is less than an ISO year, but the given dates are in different calendar years', function () {
+      const result = differenceInISOWeekYears(
+        new Date(2012, 0 /* Jan */, 2),
+        new Date(2012, 0 /* Jan */, 1)
+      )
+      assert(result === 0)
+    })
+
+    it('the same for the swapped dates', function () {
+      const result = differenceInISOWeekYears(
+        new Date(2012, 0 /* Jan */, 1),
+        new Date(2012, 0 /* Jan */, 2)
+      )
+      assert(result === 0)
+    })
+
+    it('the ISO weeks and weekdays of the given dates are the same', function () {
+      const result = differenceInISOWeekYears(
+        new Date(2013, 11 /* Dec */, 30),
+        new Date(2012, 0 /* Jan */, 2)
+      )
+      assert(result === 2)
+    })
+
+    it('the given dates are the same', function () {
+      const result = differenceInISOWeekYears(
+        new Date(2014, 8 /* Sep */, 5, 0, 0),
+        new Date(2014, 8 /* Sep */, 5, 0, 0)
+      )
+      assert(result === 0)
+    })
+
+    it('does not return -0 when the given dates are the same', () => {
+      function isNegativeZero(x: number): boolean {
+        return x === 0 && 1 / x < 0
+      }
+
+      const result = differenceInISOWeekYears(
+        new Date(2014, 8 /* Sep */, 5, 0, 0),
+        new Date(2014, 8 /* Sep */, 5, 0, 0)
+      )
+
+      const resultIsNegative = isNegativeZero(result)
+      assert(resultIsNegative === false)
+    })
+  })
+
+  it('returns NaN if the first date is `Invalid Date`', function () {
+    const result = differenceInISOWeekYears(
+      new Date(NaN),
+      new Date(2017, 0 /* Jan */, 1)
+    )
+    assert(isNaN(result))
+  })
+
+  it('returns NaN if the second date is `Invalid Date`', function () {
+    const result = differenceInISOWeekYears(
+      new Date(2017, 0 /* Jan */, 1),
+      new Date(NaN)
+    )
+    assert(isNaN(result))
+  })
+
+  it('returns NaN if the both dates are `Invalid Date`', function () {
+    const result = differenceInISOWeekYears(new Date(NaN), new Date(NaN))
+    assert(isNaN(result))
+  })
+
+  it('throws TypeError exception if passed less than 2 arguments', function () {
+    assert.throws(differenceInISOWeekYears.bind(null), TypeError)
+    assert.throws(differenceInISOWeekYears.bind(null, 1), TypeError)
+  })
+})