ApplicationController.swift

// declare WKUIDelegate as a delegate for ApplicationController 

lazy var session: TLSession = {
    let session = TLSession(webViewConfiguration: self.webViewConfiguration)
    session.delegate = self
    session.webView.UIDelegate = self // add this
    return session
}()

// MARK: WKUIDelegate

func webView(webView: WKWebView, runJavaScriptAlertPanelWithMessage message: String, initiatedByFrame frame: WKFrameInfo, completionHandler: () -> Void) {
    let alertController = UIAlertController(title: nil, message: message, preferredStyle: .Alert)
    let defaultAction = UIAlertAction(title: "OK", style: .Default, handler: nil)
    alertController.addAction(defaultAction)
    presentViewController(alertController, animated: true, completion: completionHandler)
}

func webView(webView: WKWebView, runJavaScriptConfirmPanelWithMessage message: String, initiatedByFrame frame: WKFrameInfo, completionHandler: (Bool) -> Void) {
    let alertController = UIAlertController(title: nil, message: message, preferredStyle: .Alert)
    let cancelAction = UIAlertAction(title: "Cancel", style: .Default, handler: {(UIAlertAction) in completionHandler(false) })
    let confirmAction = UIAlertAction(title: "OK", style: .Default, handler: {(UIAlertAction) in completionHandler(true) })
    alertController.addAction(cancelAction)
    alertController.addAction(confirmAction)
    presentViewController(alertController, animated: true, completion: nil)
}

func webView(webView: WKWebView, runJavaScriptTextInputPanelWithPrompt prompt: String, defaultText: String?, initiatedByFrame frame: WKFrameInfo, completionHandler: (String?) -> Void) {
    let alertController = UIAlertController(title: nil, message: prompt, preferredStyle: .Alert)
    let cancelAction = UIAlertAction(title: "Cancel", style: .Default, handler: {(UIAlertAction) in completionHandler(nil)})
    let confirmAction = UIAlertAction(title: "OK", style: .Default, handler: {(UIAlertAction) in
        let textField = alertController.textFields![0] as UITextField
        completionHandler(textField.text)
    })
    alertController.addTextFieldWithConfigurationHandler({(textField) in textField.text = defaultText})
    alertController.addAction(cancelAction)
    alertController.addAction(confirmAction)
    presentViewController(alertController, animated: true, completion: nil)
}