extension WKWebView {

    func contentSize(completion : @escaping (_ size: CGSize?, _ error: Error?) -> ()){
        self.evaluateJavaScript("document.body.scrollHeight;") { (scrollHeight, error) in
            if let height = scrollHeight as? CGFloat {
                self.evaluateJavaScript("document.body.scrollWidth;") { (scrollWidth, error) in
                    if let width = scrollWidth as? CGFloat {
                        let sizeThatFits = self.sizeThatFits(.zero)
                        let widthPercentage = (width / sizeThatFits.width) * 100
                        let requiredHeight = (height / widthPercentage) * 100
                        let size = CGSize.init(width: sizeThatFits.width, height: requiredHeight)
                        completion(size, nil)
                    } else {
                        completion(nil, error)
                    }
                }
            } else {
                completion(nil, error)
            }
        }
    }

}