WKUserScript not working

Question

I want to inject a script using WKWebview API. For some reason it isn't working and I can't figure it out. I've tried debugging in Safari developer console and I can't find the JavaScript code in there either.

Implementation Code as follows:

NSString *js = @"document.body.style.background = \"#FF0000\";";

    NSString *myScriptSource = @"alert('Hello, World!')";


    WKUserScript *s = [[WKUserScript alloc] initWithSource:myScriptSource injectionTime:WKUserScriptInjectionTimeAtDocumentStart forMainFrameOnly:YES];
    WKUserContentController *c = [[WKUserContentController alloc] init];
    [c addUserScript:s];

    WKWebViewConfiguration *conf = [[WKWebViewConfiguration alloc] init];
    conf.userContentController = c;

    WKWebView *webview = [[WKWebView alloc] initWithFrame:self.view.bounds configuration:conf];
    [self.view addSubview:webview];
    webview.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    // Do any additional setup after loading the view, typically from a nib.
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.com"]];
        [webview loadRequest:request];
    });

Answer 1

alert isn't implemented in WKWebView by default, so even if your user script runs it won't visibly do anything. You need to implement runJavaScriptAlertPanelWithMessage:

func webView(_ webView: WKWebView, runJavaScriptAlertPanelWithMessage message: String, initiatedByFrame frame: WKFrameInfo, completionHandler: @escaping (() -> Void)) {
  let alert = UIAlertController.create(title: frame.request.url?.host, message: message, preferredStyle: .alert)
  alert.addAction(UIAlertAction(title: "OK", style: .default, handler: { action in
    completionHandler()
  }))
  present(alert, animated: true, completion: nil)
}

I don't think the injected JavaScript actually appears in the DOM anywhere, it's a property internal to the WKWebView.