Parse 'YYYY' correctly

[dyoshikawa]

When only 'YYYY', parsed result was incorrect.

TZ=Asia/Tokyo yarn jest ./test/parse.test.js

Output:

  ● Parse › moment-js like formatted dates

    expect(received).toBe(expected) // Object.is equality
    
    Expected value to be:
      "2018-01-01T00:00:00+09:00"
    Received:
      "2018-01-01T09:00:00+09:00"

      37 |     expect(dayjs(d).valueOf()).toBe(moment(d).valueOf()) // not recommend
      38 |     d = '2018'
    > 39 |     expect(dayjs(d).format()).toBe(moment(d).format()) // not recommend
      40 |     d = '2018-05-02T11:12:13Z' // should go direct to new Date() rather our regex
      41 |     expect(dayjs(d).format()).toBe(moment(d).format()) // not recommend
      42 |   })
      
      at Object.<anonymous> (test/parse.test.js:39:31)

Failed this test in my local env which is in Asia/tokyo time zone.

Compare dayjs and moment:

// TZ=Asia/Tokyo

import dayjs from 'dayjs'
import moment from 'moment'

console.log(dayjs('2018').format())
// 2018-01-01T09:00:00+09:00

console.log(moment('2018').format())
// 2018-01-01T00:00:00+09:00

So I think expected behavior: 2018-01-01T00:00:00+09:00 .

[codecov]

Codecov Report

Merging #969 into dev will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               dev      #969   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          169       169           
  Lines         1429      1430    +1     
  Branches       305       306    +1     
=========================================
+ Hits          1429      1430    +1     

Impacted Files	Coverage Δ
src/constant.js	100.00% <100.00%> (ø)
src/index.js	100.00% <100.00%> (ø)

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[dyoshikawa]

If d[2] was undefined, set default value.

[iamkun]

const _m = d[2] - 1 || 0

[dyoshikawa]

Thanks. I adopted it.