Nostr Event Filter Example

filter.ts

/** Basic implementation of NIP 01 filters in typescript. */

interface Event {
  id         : string
  kind       : number
  created_at : number
  pubkey     : string
  subject   ?: string
  content    : string
  sig        : string
  tags       : string[][]
}

interface Filter {
  ids       ?: string[]
  authors   ?: string[]
  kinds     ?: number[]
  since     ?: number
  until     ?: number
  limit     ?: number
  [ key : string ] : string | number | string[] | number[] | undefined
}


export function filterEvents (
  events : Event[],
  filter : Filter = {}
) : Event[] {
  const { authors, ids, kinds, since, until, limit, ...rest } = filter

  events.sort((a, b) => b.created_at - a.created_at)

  if (limit !== undefined && limit < events.length) {
    events = events.slice(0, limit)
  }

  if (ids !== undefined) {
    events = events.filter(e => ids.includes(e.id))
  }

  if (since !== undefined) {
    events = events.filter(e => e.created_at > since)
  }

  if (until !== undefined) {
    events = events.filter(e => e.created_at < until)
  }

  if (authors !== undefined) {
    events = events.filter(e => authors.includes(e.pubkey))
  }

  if (kinds !== undefined) {
    events = events.filter(e => kinds.includes(e.kind))
  }

  for (const key in rest) {
    if (key.startsWith('#')) {
      const tag  = key.slice(1, 2)
      const keys = rest[key]
      events = events.filter(e => {
        return e.tags.some(t => {
          return t[0] === tag && keys.includes(t[1])
        })
      })
    }
  }

  return events
}