message: feat(nested-scroll): add destory logic
diff: @@ -69,6 +69,7 @@ export default class NestedScroll {
  }
  singleton.appendBScroll(scroll)
  + this.addHooks(scroll)
  return singleton
  }
  @@ -76,6 +77,11 @@ export default class NestedScroll {
  private initStores(): void {
  this.stores = []
  }
  + private addHooks(scroll: BScroll): void {
  + scroll.on('destroy', () => {
  + this.removeBScroll(scroll)
  + })
  + }
  appendBScroll(scroll: BScroll): void {
  this.stores.push(scroll)
  @@ -83,11 +89,25 @@ export default class NestedScroll {
  this.handleCompatible()
  }
  + removeBScroll(scroll: BScroll): void {
  + const index = this.stores.indexOf(scroll)
  + if (index === -1) return
  + this.stores.splice(index, 1)
  + this.handleContainRelationship()
  + this.handleCompatible()
  + }
  +
  private handleContainRelationship(): void {
  // bs's length <= 1
  - if (this.stores.length <= 1) return
  -
  const stores = this.stores
  + if (stores.length <= 1) {
  + // there is only a childBScroll left.
  + if (stores[0] && stores[0].__parentInfo) {
  + stores[0].__parentInfo = undefined
  + }
  + return
  + }
  +
  let outerBS
  let outerBSWrapper
  let innerBS
  