Example

import ExpoModulesCore

@Record
struct DownloadOptions {
  var url: URL              // required
  var retries: Int = 3      // omittable, default 3
  var label: String?        // omittable and nullable
}

public final class DownloaderModule: Module {
  private var volume: Double = 1

  public func definition() -> ModuleDefinition {
    Name("Downloader")

    Events("onProgress")

    OnStartObserving {
      self.beginProgressUpdates()
    }

    OnStopObserving {
      self.stopProgressUpdates()
    }

    Constant("buildInfo") { computeBuildInfo() }

    Function("clamp") { (value: Double) -> Double in
      return min(max(value, 0), 1)
    }

    Property("volume") { self.volume }
      .set { self.volume = $0 }

    AsyncFunction("download") { (options: DownloadOptions) -> String in
      return try await self.performDownload(options)
    }

    AsyncFunction("clearCache") {
      try FileManager.default.removeItem(at: self.cacheDirectory)
    }
  }

  private func report(percent: Double) {
    sendEvent("onProgress", ["percent": percent])
  }
}

import ExpoModulesCore

@Record
struct DownloadOptions {
  var url: URL
  var retries: Int = 3
  var label: String?
}

@ExpoModule("Downloader")
public final class DownloaderModule: Module {
  // Explicit wire name: default @Event would strip "on" and emit "progress".
  @Event("onProgress")
  var onProgress: (ProgressEvent) -> Void

  @JS("clamp")
  func clamp(value: Double) -> Double {
    return min(max(value, 0), 1)
  }

  // Stored var -> JS getter + setter, matching the 1.0 get/set pair.
  @JS
  var volume: Double = 1

  // A let is a natural constant: read-only from JS.
  @JS
  let buildInfo = computeBuildInfo()

  @JS
  func download(options: DownloadOptions) async throws -> String {
    return try await performDownload(options)
  }

  // override: the hooks are inherited from the Module base class.
  override func didStartListening(event: String) {
    beginProgressUpdates()
  }

  override func didStopListening(event: String) {
    stopProgressUpdates()
  }

  // Kept on the DSL: the body blocks without suspending, and a 2.0 async
  // member would start it on the JS actor instead of a background queue.
  public func definition() -> ModuleDefinition {
    AsyncFunction("clearCache") {
      try FileManager.default.removeItem(at: self.cacheDirectory)
    }
  }

  private func report(percent: Double) {
    onProgress(ProgressEvent(percent: percent))
  }
}

@Record
struct ProgressEvent {
  var percent: Double
}

import ExpoModulesCore

@Record
struct DownloadOptions {
  var url: URL
  var retries: Int = 3
  var label: String?
}

@Record
struct ProgressEvent {
  var percent: Double
}

@ExpoModule("Downloader")
public final class DownloaderModule: Module {
  @Event("onProgress")
  var onProgress: (ProgressEvent) -> Void

  @JS("clamp")
  func clamp(value: Double) -> Double {
    return min(max(value, 0), 1)
  }

  @JS
  var volume: Double = 1

  @JS
  let buildInfo = computeBuildInfo()

  @JS
  func download(options: DownloadOptions) async throws -> String {
    return try await performDownload(options)
  }

  @JS
  func clearCache() async throws {
    // Explicit hop: the body blocks, so it must not run on the JS actor.
    try await Task.detached {
      try FileManager.default.removeItem(at: self.cacheDirectory)
    }.value
  }

  override func didStartListening(event: String) {
    beginProgressUpdates()
  }

  override func didStopListening(event: String) {
    stopProgressUpdates()
  }

  private func report(percent: Double) {
    onProgress(ProgressEvent(percent: percent))
  }
}