4 files changed, 183 insertions, 0 deletions
diff --git a/date-fns/src/milliseconds/index.d.ts b/date-fns/src/milliseconds/index.d.ts
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--- /dev/null
+++ b/date-fns/src/milliseconds/index.d.ts
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+// This file is generated automatically by `scripts/build/typings.js`. Please, don't change it.
+
+import { milliseconds } from 'date-fns'
+export default milliseconds
diff --git a/date-fns/src/milliseconds/index.js.flow b/date-fns/src/milliseconds/index.js.flow
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+++ b/date-fns/src/milliseconds/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: (duration: Duration) => number
diff --git a/date-fns/src/milliseconds/index.ts b/date-fns/src/milliseconds/index.ts
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+++ b/date-fns/src/milliseconds/index.ts
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+import requiredArgs from '../_lib/requiredArgs/index'
+import { Duration } from '../types'
+
+// Leap year occures every 4 years, except for years that are divisable by 100 and not divisable by 400.
+// 1 mean year = (365+1/4-1/100+1/400) days = 365.2425 days
+const daysInYear = 365.2425
+
+/**
+ * @name milliseconds
+ * @category Millisecond Helpers
+ * @summary
+ * Returns the number of milliseconds in the specified, years, months, weeks, days, hours, minutes and seconds.
+ *
+ * @description
+ * Returns the number of milliseconds in the specified, years, months, weeks, days, hours, minutes and seconds.
+ *
+ * One years equals 365.2425 days according to the formula:
+ *
+ * > Leap year occures every 4 years, except for years that are divisable by 100 and not divisable by 400.
+ * > 1 mean year = (365+1/4-1/100+1/400) days = 365.2425 days
+ *
+ * One month is a year divided by 12.
+ *
+ * @param {Duration} duration - the object with years, months, weeks, days, hours, minutes and seconds to be added. Positive decimals will be rounded using `Math.floor`, decimals less than zero will be rounded using `Math.ceil`.
+ * @returns {number} the milliseconds
+ * @throws {TypeError} 1 argument required
+ *
+ * @example
+ * // 1 year in milliseconds
+ * milliseconds({ years: 1 })
+ * //=> 31556952000
+ *
+ * // 3 months in milliseconds
+ * milliseconds({ months: 3 })
+ * //=> 7889238000
+ */
+export default function milliseconds({
+  years,
+  months,
+  weeks,
+  days,
+  hours,
+  minutes,
+  seconds,
+}: Duration): number {
+  requiredArgs(1, arguments)
+
+  let totalDays = 0
+
+  if (years) totalDays += years * daysInYear
+  if (months) totalDays += months * (daysInYear / 12)
+  if (weeks) totalDays += weeks * 7
+  if (days) totalDays += days
+
+  let totalSeconds = totalDays * 24 * 60 * 60
+
+  if (hours) totalSeconds += hours * 60 * 60
+  if (minutes) totalSeconds += minutes * 60
+  if (seconds) totalSeconds += seconds
+
+  return Math.round(totalSeconds * 1000)
+}
diff --git a/date-fns/src/milliseconds/test.ts b/date-fns/src/milliseconds/test.ts
new file mode 100644
index 0000000..e576c23
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+++ b/date-fns/src/milliseconds/test.ts
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+// @flow
+/* eslint-env mocha */
+
+import assert from 'assert'
+import milliseconds from '.'
+
+describe('milliseconds', () => {
+  it('converts years to milliseconds', () => {
+    const result = milliseconds({ years: 2 })
+    assert(result === 63113904000)
+  })
+
+  it('converts months to milliseconds', () => {
+    const result = milliseconds({ months: 3 })
+    assert(result === 7889238000)
+  })
+
+  it('converts weeks to milliseconds', () => {
+    const result = milliseconds({ weeks: 2 })
+    assert(result === 1209600000)
+  })
+
+  it('converts days to milliseconds', () => {
+    const result = milliseconds({ days: 5 })
+    assert(result === 432000000)
+  })
+
+  it('converts hours to milliseconds', () => {
+    const result = milliseconds({ hours: 2 })
+    assert(result === 7200000)
+  })
+
+  it('converts minutes to milliseconds', () => {
+    const result = milliseconds({ minutes: 5 })
+    assert(result === 300000)
+  })
+
+  it('converts seconds to milliseconds', () => {
+    const result = milliseconds({ seconds: 10 })
+    assert(result === 10000)
+  })
+
+  it('sums all the duration values', () => {
+    const result = milliseconds({
+      years: 2,
+      months: 3,
+      weeks: 2,
+      days: 5,
+      hours: 2,
+      minutes: 5,
+      seconds: 10
+    })
+    assert(result === 72652252000)
+  })
+
+  it('returns 0 for an empty duration', () => {
+    const result = milliseconds({})
+    assert(result === 0)
+  })
+
+  it('throws TypeError exception if passed less than 1 argument', function() {
+    // @ts-expect-error
+    assert.throws(milliseconds.bind(null), TypeError)
+  })
+})