fix(diff): allow .diff(unit) shorthand for diffing with current time

src/index.js

@@ -348,7 +348,13 @@ class Dayjs {
   }
 
   diff(input, units, float) {
-    const unit = Utils.p(units)
+    let unit
+    if (typeof input === 'string' && !units) {
+      unit = Utils.p(input)
+      input = dayjs()
+    } else {
+      unit = Utils.p(units)
+    }
     const that = dayjs(input)
     const zoneDelta = (that.utcOffset() - this.utcOffset()) * C.MILLISECONDS_A_MINUTE
     const diff = this - that

test/display.test.js

@@ -1,8 +1,8 @@
-import moment from 'moment'
 import MockDate from 'mockdate'
+import moment from 'moment'
 import dayjs from '../src'
-import th from '../src/locale/th'
 import '../src/locale/ja'
+import th from '../src/locale/th'
 
 beforeEach(() => {
   MockDate.set(new Date())
@@ -219,6 +219,14 @@ describe('Difference', () => {
   it('undefined edge case', () => {
     expect(dayjs().diff(undefined, 'seconds')).toBeDefined()
   })
+
+  it('diff with the current time if no date is supplied', () => {
+    const base = dayjs().add(36, 'hour')
+    const units = ['seconds', 'minutes', 'hours', 'days', 'weeks', 'months', 'quarters', 'years']
+    units.forEach((u) => {
+      expect(base.diff(u)).toBe(base.diff(dayjs(), u))
+    })
+  })
 })
 
 it('Unix Timestamp (milliseconds)', () => {