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
}

There is now search field: https://github.com/nostr-protocol/nips/blob/master/50.md

Thanks for posting this. Is NIP-50 considered a mandatory part of the spec now?

Nope, it is optional, just notifying

I should also mention that this script does not do partial matching of event ids or pubkeys, which is in the filter spec. To add partial matching to authors as an example, you can iterate through authors and check if e.pubkey.startsWith(author).