filter based on objects

[andredewaard]

Is something like this possible, or any idea how to do this in any other way?

  const chapter = { type: 'chapter' as const }
  const section = { type: 'section' as const }
  const items = [chapter, section]
  const filteredItems = items.filter((item) => item.type === 'chapter')

Result is:

const filteredItems: ({
    type: "chapter";
} | {
    type: "section";
})[]

but should be:

const filteredItems: {
    type: "chapter";
}[]

[mattpocock]

Unfortunately not, TS can't detect that unless you use a type predicate.

[andredewaard]

So the only option would be ?

  const filteredItems = items.filter((item) => item.type === 'chapter') as Array<typeof chapter>

[mattpocock]

Or:

https://www.totaltypescript.com/tips/type-predicates