WKWebViewController.swift

import UIKit
import WebKit

class WKWebViewController: UIViewController {

    var request: URLRequest?
    weak var uiDelegate: WKUIDelegate?
    weak var navigationDelegate: WKNavigationDelegate?

    lazy var webView: WKWebView = {
        let config = WKWebViewConfiguration()

        let webView = WKWebView(frame: .zero, configuration: config)
        webView.uiDelegate = self.uiDelegate
        webView.navigationDelegate = self.navigationDelegate
        return webView
    }()

    private lazy var heightConstraint: NSLayoutConstraint = webView.heightAnchor.constraint(equalToConstant: 0)

    init(request: URLRequest? = nil, uiDelegate: WKUIDelegate? = nil, navigationDelegate: WKNavigationDelegate? = nil) {
        self.request = request
        super.init(nibName: nil, bundle: nil)
        self.uiDelegate = uiDelegate ?? self
        self.navigationDelegate = navigationDelegate ?? self
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(webView, constraints: .allEdges())
        heightConstraint.isActive = true

        if let request = self.request {
            webView.load(request)
        }
    }
}

extension WKWebViewController: WKNavigationDelegate {
    func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
        webView.evaluateJavaScript("document.readyState", completionHandler: { [weak self] (complete, error) in
            if complete != nil {
                self?.heightConstraint.constant = webView.scrollView.contentSize.height
            }
        })
    }
}

extension WKWebViewController: WKUIDelegate {

}