executing javascript on WKWebView

ViewController.swift

import UIKit
import WebKit

class ViewController: UIViewController, WKNavigationDelegate {

	let webView = WKWebView(frame: CGRectMake(0, 0, 1024, 720))
	
	override func viewDidLoad() {
		super.viewDidLoad()
		webView.navigationDelegate = self
	}
	
	
	override func viewDidAppear(animated: Bool) {
		super.viewDidAppear(animated)
		
		let req = NSURLRequest(URL: NSURL(string: "https://google.com")!)
		
		webView.loadRequest(req)
	}
	
	func webView(webView: WKWebView, didFinishNavigation navigation: WKNavigation!) {
		
		let jsString = "document.title"
		
		webView.evaluateJavaScript(jsString) { (result, error) -> Void in
			print("result \(result)")
		}
	}

}