Native events

Native-to-JS subscriptions from Swift and Kotlin sources

A method whose only parameter is a callback is a subscription, not a call. Calling it from JavaScript returns an unsubscribe function. Native posts each payload over the one event bridge and the listener receives the decoded values.

@MainActor final class Clock: PeachModule {
  init() {}

  private var tick: ((Double) -> Void)?
  func onTick(_ callback: @escaping (Double) -> Void) {
    tick = callback
  }
}

object Clock : OneModule {
    private var tick: ((Double) -> Unit)? = null
    fun onTick(callback: (Double) -> Unit) {
        tick = callback
    }
}

import { Clock } from './native/Clock.swift'

const unsubscribe = Clock.onTick((at) => {
  console.log('tick', at)
})
unsubscribe()

The callback may take zero or more parameters; each one decodes with the same wire rules as method arguments, so structs, enums, Date and Data payloads revive before the listener runs. Pass a real function: anything else throws before the subscription leaves JavaScript. Calling the returned function removes the JavaScript listener, so call it when the component unmounts.

Native keeps its own stored closure, so the author owns the native side of the lifecycle: emitting after every JavaScript listener unsubscribed posts to nobody, and a closure the author never releases stays retained. Under the Peach simulator there is no JavaScript runtime to receive an event, so emitted events queue in the module instead: the simulator host drains them with the peach_poll_events export, which returns a length-prefixed JSON array of { channel, args } pairs using the same framing as peach_call_poll.