Js immutable - 如何将 map 展平为 Set<number></number>

Question

我有一个Map<number, Shipment>类型的值 shipments，Shipment 有一个Set<number>类型的属性packageIds 。 当我有多个货件时，我想 go 通过每个货件，获取他们的packageIds并使用每个货件中的所有packageIds制作一个新的平面集：

shipments.flatMap(shipment => shipment.get('packageIds'))

但是，如果我这样做，我会收到 typescript 错误：

TS2322: Type 'Set<number>' is not assignable to type 'Iterable<[unknown, unknown]>'.
  The types returned by '[Symbol.iterator]().next(...)' are incompatible between these types. 
  Type 'IteratorResult<number, any>' is not assignable to type 'IteratorResult<[unknown, unknown], any>'.       
  Type 'IteratorYieldResult<number>' is not assignable to type 'IteratorResult<[unknown, unknown], any>'.         
  Type 'IteratorYieldResult<number>' is not assignable to type 'IteratorYieldResult<[unknown, unknown]>'.           
  Type 'number' is not assignable to type '[unknown, unknown]'. 

当遍历 map 时，我怎样才能得到一个平面集？

Answer 1

Map的 immutablejs flatMap方法返回另一个Map 。 那不是你想要的。 之前转换为Set ，丢弃Map键：

shipments.toSet().flatMap(shipment => shipment.get('packageIds'))