feat: Add negative years support

src/plugin/negativeYear/index.js

@@ -0,0 +1,23 @@
+export default (_, c, dayjs) => {
+  const proto = c.prototype
+
+  const parseDate = (cfg) => {
+    const { date } = cfg
+    if (typeof date === 'string' && date.charAt(0) === '-') {
+      const newDate = new Date(date.slice(1))
+      const fullYear = newDate.getFullYear()
+      if (date.indexOf(`-${fullYear}`) !== -1) {
+        return dayjs(newDate).subtract(fullYear * 2, 'year').toDate()
+      }
+      return date
+    }
+    return date
+  }
+
+  const oldParse = proto.parse
+  proto.parse = function (cfg) {
+    cfg.date = parseDate.bind(this)(cfg)
+    oldParse.bind(this)(cfg)
+  }
+}
+

test/plugin/negativeYear.test.js

@@ -0,0 +1,52 @@
+import MockDate from 'mockdate'
+import dayjs from 'dayjs'
+import negativeYear from '../../src/plugin/negativeYear'
+import utc from '../../src/plugin/utc'
+import { REGEX_PARSE } from '../../src/constant'
+
+
+dayjs.extend(negativeYear)
+dayjs.extend(utc)
+
+beforeEach(() => {
+  MockDate.set(new Date())
+})
+
+afterEach(() => {
+  MockDate.reset()
+})
+
+describe('negativeYear', () => {
+  it('parses negative years', () => {
+    expect(dayjs('-2020-01-01').year()).toBe(-2020)
+    const date = '-2021/01/03'
+    const date2 = '01/03/-2021'
+    const date3 = '01-03--2021'
+    const d = date.match(REGEX_PARSE)
+    expect(dayjs(date).format('YYYY-MM-DD')).toBe('-2021-01-03')
+    expect(dayjs(date2).format('YYYY-MM-DD')).toBe('Invalid Date')
+    expect(dayjs(date3).format()).toBe('Invalid Date')
+    expect(d).toBe(null)
+  })
+
+  it('does not parse non-negative years', () => {
+    expect(dayjs('2020-01-01').year()).toBe(2020)
+  })
+
+  it('works with other plugins', () => {
+    expect(dayjs.utc('-2020-01-01').year()).toBe(-2020)
+  })
+
+  it('Add and subtract with negative years', () => {
+    expect(dayjs('-2006').add(1, 'y')).toEqual(dayjs('-2005'))
+    expect(dayjs('-2006').subtract(1, 'y')).toEqual(dayjs('-2007'))
+    expect(dayjs('-2006').add(1, 'y').format('YYYY')).toBe(dayjs('-2005').format('YYYY'))
+    expect(dayjs('-2006').subtract(1, 'y').format('YYYY')).toBe(dayjs('-2007').format('YYYY'))
+  })
+
+  it('Compare date with negative years', () => {
+    expect(dayjs('-2006').isAfter(dayjs('-2007'))).toBeTruthy()
+    expect(dayjs('-2006').isBefore(dayjs('-2005'))).toBeTruthy()
+    expect(dayjs('-2006').isSame('-2006')).toBeTruthy()
+  })
+})

types/plugin/negativeYear.d.ts

@@ -0,0 +1,4 @@
+import {PluginFunc} from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin