How can I make a countdown with NSTimer?

In Swift 5.1 this will work:

var counter = 30

override func viewDidLoad() {
    super.viewDidLoad()

    Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(updateCounter), userInfo: nil, repeats: true)
}



@objc func updateCounter() {
    //example functionality
    if counter > 0 {
        print("\(counter) seconds to the end of the world")
        counter -= 1
    }
}