Calling Swift from JavaScript

I am new to Swift/iOS and have been working on an app that calls Swift code from JavaScript. There are not as many tutorials online and a lot of them are from when Swift was still in beta. Anyway, I was getting an error on my code and I am unable to compile it and I was wondering if any one had any tips and best practices when it comes to calling swift code from JavaScript.

Here is my code

import UIKit
import WebKit

class ViewController: UIViewController, WKScriptMessageHandler {

    @IBOutlet var containerView : UIView! = nil

    var webView: WKWebView?

    override func loadView() {
        super.loadView()


        var contentController = WKUserContentController();
        var userScript = WKUserScript(
            source: "redHeader()",
            injectionTime: WKUserScriptInjectionTime.AtDocumentEnd,
            forMainFrameOnly: true
        )
        contentController.addUserScript(userScript)
        contentController.addScriptMessageHandler(
            self,
            name: "callbackHandler"
        )

        var config = WKWebViewConfiguration()
        config.userContentController = contentController

        self.webView = WKWebView(frame: self.view.frame, configuration: config)
        self.view = self.webView!
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        var url = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("index", ofType: "html")!)
        var req = NSURLRequest(URL: url!)
        self.webView!.loadRequest(req)
    }

    func userContentController(userContentController: WKUserContentController!,didReceiveScriptMessage message: WKScriptMessage!) {
        if(message.name == "callbackHandler") {
            println("JavaScript is sending a message \(message.body)")
        } }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

The error is on class ViewController: UIViewController, WKScriptMessageHandler { and it says

Type 'ViewController' does not conform to protocol 'WKScriptMessageHandler'.

Any help would be greatly appreciated.