WKWebView evaluateJavaScript not returning html - ios

Question

I am trying to parse the html returned from a WKWebView load() with evaluateJavaScript but it never prints anything. Am I doing this right? Any other ways? didFinish does print.
import UIKit
import WebKit
class MyWebViewController: UIViewController, WKNavigationDelegate {
var webView: WKWebView!
override func viewDidLoad() {
super.viewDidLoad()
webView = WKWebView(frame: self.view.frame)
webView.navigationDelegate = self
let url = NSURL (string: "https://google.com");
let request = NSURLRequest(url: url! as URL)
webView.load(request as URLRequest)
self.view.addSubview(webView)
self.view.sendSubview(toBack: webView)
}
func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
webView.evaluateJavaScript("document.documentElement.outerHTML.toString()", completionHandler: { (html: AnyObject?, error: NSError?) in
print(html!)
} as? (Any?, Error?) -> Void)
print("didFinish")
}
}

Answer 1

Using evaluateJavaScript with a WKWebView is a bit tricky.
Since I think this answer would be useful to many people, rather than address your specific question with a short code snippet and a comment that you need to implement WKScriptMessageHandler, I'm going to post a full, complete example that you can use to see how everything works together.
To use this, create a "Single View Application" iOS project in Xcode and paste this over the default ViewController.swift file.
//
// WebViewController.swift
// WKWebViewExample
//
// Created by par on 4/2/17.
// Copyright © 2017 par. All rights reserved. MIT License.
//
import UIKit
import WebKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let webViewController = WebViewController()
// install the WebViewController as a child view controller
addChildViewController(webViewController)
let webViewControllerView = webViewController.view!
view.addSubview(webViewControllerView)
webViewControllerView.translatesAutoresizingMaskIntoConstraints = false
webViewControllerView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
webViewControllerView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
webViewControllerView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
webViewControllerView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
webViewController.didMove(toParentViewController: self)
}
}
class WebViewController: UIViewController, WKNavigationDelegate, WKScriptMessageHandler {
private var webView: WKWebView!
private var webViewContentIsLoaded = false
init() {
super.init(nibName: nil, bundle: nil)
self.webView = {
let contentController = WKUserContentController()
contentController.add(self, name: "WebViewControllerMessageHandler")
let configuration = WKWebViewConfiguration()
configuration.userContentController = contentController
let webView = WKWebView(frame: .zero, configuration: configuration)
webView.scrollView.bounces = false
webView.navigationDelegate = self
return webView
}()
}
required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") }
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(webView)
webView.translatesAutoresizingMaskIntoConstraints = false
webView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
webView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
webView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
webView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
if !webViewContentIsLoaded {
let url = URL(string: "https://stackoverflow.com")!
let request = URLRequest(url: url)
webView.load(request)
webViewContentIsLoaded = true
}
}
private func evaluateJavascript(_ javascript: String, sourceURL: String? = nil, completion: ((_ error: String?) -> Void)? = nil) {
var javascript = javascript
// Adding a sourceURL comment makes the javascript source visible when debugging the simulator via Safari in Mac OS
if let sourceURL = sourceURL {
javascript = "//# sourceURL=\(sourceURL).js\n" + javascript
}
webView.evaluateJavaScript(javascript) { _, error in
completion?(error?.localizedDescription)
}
}
// MARK: - WKNavigationDelegate
func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
// This must be valid javascript! Critically don't forget to terminate statements with either a newline or semicolon!
let javascript =
"var outerHTML = document.documentElement.outerHTML.toString()\n" +
"var message = {\"type\": \"outerHTML\", \"outerHTML\": outerHTML }\n" +
"window.webkit.messageHandlers.WebViewControllerMessageHandler.postMessage(message)\n"
evaluateJavascript(javascript, sourceURL: "getOuterHMTL")
}
// MARK: - WKScriptMessageHandler
func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
guard let body = message.body as? [String: Any] else {
print("could not convert message body to dictionary: \(message.body)")
return
}
guard let type = body["type"] as? String else {
print("could not convert body[\"type\"] to string: \(body)")
return
}
switch type {
case "outerHTML":
guard let outerHTML = body["outerHTML"] as? String else {
print("could not convert body[\"outerHTML\"] to string: \(body)")
return
}
print("outerHTML is \(outerHTML)")
default:
print("unknown message type \(type)")
return
}
}
}

Answer 2

I know it has been a while since this was answered and I found that this didn't really work for me. I used the below instead.
I could not get the evaluateJavaScript to work until i added the setTimeout() function. For what it is worth here is my code below.
webView.evaluateJavaScript("setTimeout(function(){
// Do something here
},10);") { (result1, error) in
if error == nil {
print(result1 ?? "")
}
}