如果您等到页面加载完毕，则可以使用：

webView.evaluateJavaScript("document.documentElement.outerHTML.toString()", 
                           completionHandler: { (html: Any?, error: Error?) in
    print(html)
})

您还可以注入一些JavaScript，使您返回HTML。

let script = WKUserScript(source: javascriptString, injectionTime: injectionTime, forMainFrameOnly: true)
userContentController.addUserScript(script)
self.webView.configuration.userContentController.addScriptMessageHandler(self, name: "didGetHTML")

…

func userContentController(userContentController: WKUserContentController,
        didReceiveScriptMessage message: WKScriptMessage) {

        if message.name == "didGetHTML" {
            if let html = message.body as? String {
                print(html)
            }
        }
}

您可以注入的javascript如下所示：

webkit.messageHandlers.didGetHTML.postMessage(document.documentElement.outerHTML.toString());