webwebview could show alert windows

Ref :   https://stackoverflow.com/questions/34185339/wkwebview-javascript-confirm-and-alert-not-working

import UIKit
import WebKit

class ViewController: UIViewController, WKUIDelegate, WKNavigationDelegate {

    var wkWebView: WKWebView!

    public override func viewDidLoad() {
        super.viewDidLoad()

        wkWebView = WKWebView(frame: view.bounds, configuration: WKWebViewConfiguration())
        wkWebView.uiDelegate = self
        wkWebView.navigationDelegate = self
        view.addSubview(wkWebView!)
        let url = URL(string: "https://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_alert")!
        wkWebView.load(URLRequest(url: url))
    }

    func webView(_ webView: WKWebView,
                 runJavaScriptAlertPanelWithMessage message: String,
                 initiatedByFrame frame: WKFrameInfo,
                 completionHandler: @escaping () -> Void) {

        let alert = UIAlertController(title: nil, message: message, preferredStyle: .alert)
        let title = NSLocalizedString("OK", comment: "OK Button")
        let ok = UIAlertAction(title: title, style: .default) { (action: UIAlertAction) -> Void in
            alert.dismiss(animated: true, completion: nil)
        }
        alert.addAction(ok)
        present(alert, animated: true)
        completionHandler()
    }

    func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
        wkWebView.evaluateJavaScript("alert('Hello from evaluateJavascript()')", completionHandler: nil)
    }
}