diff --git a/src/index.js b/src/index.js
--- a/src/index.js
+++ b/src/index.js
@@ -2,16 +2,15 @@ import * as C from './constant'
 import * as Utils from './utils'
 
 const parseConfig = (config) => {
+  let reg
   if (!config) return new Date()
   if (config instanceof Date) return config
-  const configStr = String(config)
-  if (/^(\d){8}$/.test(configStr)) {
-    const y = configStr.substr(0, 4)
-    const m = configStr.substr(4, 2)
-    const d = configStr.substr(6, 2)
-    return new Date(y, m - 1, d)
-  }
-  return new Date(config) // e.g. timestamp
+  // eslint-disable-next-line no-cond-assign
+  if (reg = String(config).match(/^(\d{4})-?(\d{2})-?(\d{1,2})$/)) {
+    // 2018-08-08 or 20180808
+    return new Date(reg[1], reg[2] - 1, reg[3])
+  }
+  return new Date(config) // timestamp
 }
 
 class Dayjs {
@@ -21,8 +20,8 @@ class Dayjs {
   }
 
   init() {
-    this.timeZone = this.$d.getTimezoneOffset() / 60
-    this.timeZoneString = Utils.padStart(String(this.timeZone * -1).replace(/^(.)?(\d)/, '$10$200'), 5, '+')
+    this.$zone = this.$d.getTimezoneOffset() / 60
+    this.$zoneStr = Utils.padStart(String(this.$zone * -1).replace(/^(.)?(\d)/, '$10$200'), 5, '+')
     this.$y = this.$d.getFullYear()
     this.$M = this.$d.getMonth()
     this.$D = this.$d.getDate()
@@ -92,17 +91,20 @@ class Dayjs {
 
   startOf(units, isStartOf = true) { // isStartOf -> endOf
     const unit = Utils.prettyUnit(units)
+    const instanceFactory = (d, m, y = this.$y, isEnd = false) => {
+      const ins = new Dayjs(new Date(y, m, d))
+      return isEnd ? ins.endOf(C.D) : ins
+    }
     switch (unit) {
       case C.Y:
-        if (isStartOf) {
-          return new Dayjs(new Date(this.$y, 0, 1))
-        }
-        return new Dayjs(new Date(this.$y, 11, 31)).endOf('day')
+        return isStartOf ? instanceFactory(1, 0) :
+          instanceFactory(31, 11, this.$y, true)
       case C.M:
-        if (isStartOf) {
-          return new Dayjs(new Date(this.$y, this.$M, 1))
-        }
-        return new Dayjs(new Date(this.$y, this.$M + 1, 0)).endOf('day')
+        return isStartOf ? instanceFactory(1, this.$M) :
+          instanceFactory(0, this.$M + 1, this.$y, true)
+      case C.W:
+        return isStartOf ? instanceFactory(this.$D - this.$W, this.$M) :
+          instanceFactory(this.$D + (6 - this.$W), this.$M, this.$y, true)
       case C.D:
         if (isStartOf) {
           return new Dayjs(this.toDate().setHours(0, 0, 0, 0))
@@ -219,9 +221,9 @@ class Dayjs {
         case 'ss':
           return Utils.padStart(String(this.$s), 2, '0')
         case 'Z':
-          return `${this.timeZoneString.slice(0, -2)}:00`
+          return `${this.$zoneStr.slice(0, -2)}:00`
         default: // 'ZZ'
-          return this.timeZoneString
+          return this.$zoneStr
       }
     })
   }

diff --git a/test/manipulate.test.js b/test/manipulate.test.js
--- a/test/manipulate.test.js
+++ b/test/manipulate.test.js
@@ -10,25 +10,21 @@ afterEach(() => {
   MockDate.reset()
 })
 
-it('StartOf EndOf Year with s and upper case', () => {
-  expect(dayjs().startOf('YearS').unix()).toBe(moment().startOf('year').unix())
-  expect(dayjs().endOf('year').unix()).toBe(moment().endOf('year').unix())
-})
-
-it('StartOf EndOf Month', () => {
-  expect(dayjs().startOf('month').unix()).toBe(moment().startOf('month').unix())
-  expect(dayjs().endOf('month').unix()).toBe(moment().endOf('month').unix())
-})
+describe('StartOf EndOf', () => {
+  it('StartOf EndOf Year ... with s and upper case', () => {
+    const testArr = ['Year', 'year', 'YearS', 'month', 'day', 'week']
+    testArr.forEach((d) => {
+      expect(dayjs().startOf(d).unix()).toBe(moment().startOf(d).unix())
+      expect(dayjs().endOf(d).unix()).toBe(moment().endOf(d).unix())
+    })
+  })
 
-it('StartOf EndOf Day', () => {
-  expect(dayjs().startOf('day').unix()).toBe(moment().startOf('day').unix())
-  expect(dayjs().endOf('day').unix()).toBe(moment().endOf('day').unix())
+  it('StartOf EndOf Other -> no change', () => {
+    expect(dayjs().startOf('otherString').unix()).toBe(moment().startOf('otherString').unix())
+    expect(dayjs().endOf('otherString').unix()).toBe(moment().endOf('otherString').unix())
+  })
 })
 
-it('StartOf EndOf Other -> no change', () => {
-  expect(dayjs().startOf('otherString').unix()).toBe(moment().startOf('otherString').unix())
-  expect(dayjs().endOf('otherString').unix()).toBe(moment().endOf('otherString').unix())
-})
 
 it('Add Time days', () => {
   expect(dayjs().add(1, 's').unix()).toBe(moment().add(1, 's').unix())
diff --git a/test/parse.test.js b/test/parse.test.js
--- a/test/parse.test.js
+++ b/test/parse.test.js
@@ -9,13 +9,17 @@ beforeEach(() => {
 afterEach(() => {
   MockDate.reset()
 })
+
 describe('Parse', () => {
   it('Now', () => {
     expect(dayjs().unix()).toBe(moment().unix())
   })
 
   it('String 20130208', () => {
-    expect(dayjs('20130208').unix()).toBe(moment('20130208').unix())
+    const timeArr = ['20130108', '2018-04-24']
+    timeArr.forEach((t) => {
+      expect(dayjs(t).unix()).toBe(moment(t).unix())
+    })
   })
 
   it('String ISO 8601 date, time and zone', () => {

startOf 不支持week 选项
dayjs().startOf('week').format('YYYY-MM-DD')
dayjs().endOf('week').format('YYYY-MM-DD')

自己写下吧！我也在用这个功能
嗯，我在写。。。。
我就不fork了，直接上代码：
```javascript
//本周
 let t = dayjs()
 let val1 = t.set('date', t.$D - t.$W).add(1, 'd').format('YYYY-MM-DD') //本周第一天（周一）
 let val2 = t.set('date', t.$D + (6 - t.$W)).add(1, 'd').format('YYYY-MM-DD')  //本周最后一天（周日）
//上周
 let t = dayjs().subtract(1, 'w')
 let val1 = t.set('date', t.$D - t.$W).add(1, 'd').format('YYYY-MM-DD') //上周第一天（周一）
 let val2 = t.set('date', t.$D + (6 - t.$W)).add(1, 'd').format('YYYY-MM-DD')  //上周最后一天（周日）
```
thx, doing ...
```
    case C.W:
        let $W = null
        if (this.$W === 0) {
          $W = 6
        } else if(this.$W === 1) {
          $W = 0
        } else {
          $W = this.$W - 1
        }
        if (isStartOf) {
          return new Dayjs(new Date(this.$y, this.$M, (this.$D - $W)))
        }
        return new Dayjs(new Date(this.$y, this.$M, this.$D + (6 - $W)))
```
// add  dayjs().startOf('week')  &&  dayjs().endOf('week') support

// However,  the logic needs to be separated into good 