springButton.swift

extension UIButton {
    
    func addSpringAnimation() {
        addTarget(self, action: #selector(scaleDown), for: [.touchDown, .touchDragEnter])
        addTarget(self, action: #selector(scaleUp), for: [.touchUpInside, .touchDragExit, .touchCancel])
    }
    
    @IBAction func scaleDown(_ button: UIButton) {
        UIView.animate(withDuration: 0.1, delay: 0, options: [.allowUserInteraction, .curveLinear], animations: {
            button.transform = CGAffineTransform(scaleX: 0.75, y: 0.75)
        }, completion: nil)
    }
    
    @IBAction func scaleUp(_ button: UIButton) {
        if button.transform == .identity { return }
        UIView.animate(withDuration: 1, delay: 0, usingSpringWithDamping: 0.35, initialSpringVelocity: 0.7, options: [.allowUserInteraction, .curveLinear], animations: {
            button.transform = .identity
        }, completion: nil)
    }
    
}