React Native App Delegate in Swift 4.0

AppDelegate.swift

import UIKit

let CodeLocation = "index"
let ModuleName = "<ProjectName>"

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
  var window: UIWindow?
  
  func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil
    ) -> Bool {
    guard let codeLocation = RCTBundleURLProvider.sharedSettings().jsBundleURL(
      forBundleRoot: CodeLocation,
      fallbackResource: nil
    ),
    let rootView = RCTRootView(
      bundleURL: codeLocation,
      moduleName: ModuleName,
      initialProperties: nil,
      launchOptions: launchOptions
    )
    else {
        return false
    }
    
    let rootViewController = UIViewController()
    rootViewController.view = rootView
    
    self.window = UIWindow(frame: UIScreen.main.bounds)
    self.window?.rootViewController = rootViewController
    self.window?.makeKeyAndVisible()
    
    return true
  }
}

Add a bridging header to the project with these contents:

//
//  Use this file to import your target's public headers that you would like to expose to Swift.
//

#import <React/RCTBundleURLProvider.h>
#import <React/RCTRootView.h>
/// ... Any other React libraries that you need to access in Swift