Programmatically set the initial view controller using Storyboards

Question

How do I programmatically set the InitialViewController for a Storyboard? I want to open my storyboard to a different view depending on some condition which may

Answer 1

Swift 4, Xcode 9

in file AppDelegate.swift

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let firstVC = storyboard.instantiateViewController(withIdentifier: "firstViewController") as! firstViewController
    self.window?.rootViewController = firstVC
}