How to create a Swift method to use evaluateJavaScript with GCD - swift

Question

How do I create a macOS method that takes a URL parameter and returns HTML using evaluateJavaScript?
I want to scrape a URL that uses JavaScript, so neither String(contentsOf: url) nor URLSession.shared.dataTask(with: url) seem to work.
The code below works, but it creates a global, rather than returning a String. I want code I can reuse in other similar projects.
Can I use didSet{} or GCD DispatchGroup() and group.enter() and group.leave() to create either a class or ViewController extension to create a simple method that returns only when the page loads and the JavaScript completes? I assume I'll need a class to catch the WKNavigationDelegate calls.
I want a macOS method, not an iOS method.
Here is my working code:
ViewController.swift
import Cocoa
import WebKit
class ViewController: NSViewController, WKNavigationDelegate {
var webView: WKWebView!
var webString: String = "" {
didSet {
print("webString: \(webString.count) Bytes")
print("\(webString)")
}
}
override func viewDidLoad() {
super.viewDidLoad()
self.webView = WKWebView()
webView.navigationDelegate = self
let url = URL(string: "https://www.someWebsite.com")!
let myRequest = URLRequest(url: url)
webView.load(myRequest)
}
// WKNavigationDelegate methods
func webView(_ webView: WKWebView, didFinish: WKNavigation!) {
print(#function)
webView.evaluateJavaScript(
"document.documentElement.outerHTML.toString()",
completionHandler: { (html: Any?, error: Error?) in
self.webString = html as! String
print("In compHandler, HTML: \(self.webString.count) bytes\n")
})
}
func webView(_ webView: WKWebView, didFail: WKNavigation!, withError: Error) {
print(#function)
print("ERROR: Error=\(withError)")
}
I want something similar to this code that I use for synchronous dowloads:
func downloadDataTask(url: String) -> String {
var returnStr = ""
guard let myURL = URL(string: url) else {
showErrorAlert(
title: "ERROR: Invalid URL",
message: "Invalid URL in downloadDataTask()\n URL:'\(url)'")
return("Error: Invalid URL: '\(url)'")
}
let group = DispatchGroup()
group.enter()
let task = URLSession.shared.dataTask(with: myURL) { data, urlResponse, error in
if let myData = data {
let string = String(decoding: myData, as: UTF8.self)
returnStr = string
group.leave()
} else {
showErrorAlert(
title: "ERROR: Unable to load HTML from URL",
message: "Unable to load HTML in downloadDataTask()\n")
group.leave()
}
}
task.resume()
// wait for async completion handler task to complete
group.wait()
return(returnStr)
}
Any help would be appreciated!