iOS WKWebView not showing javascript alert() dialog

I am having some trouble getting a WKWebView in iOS 8 to display an alert dialog that is called from Javascript. After creating a standard WKWebView and loading an HTML file, I have a button on the page that creates a simple alert with some text. This works in UIWebView and in Google Chrome/Safari, but does not appear to be working in WKWebView. Any help is appreciated.

My setup is as follows:

WKWebViewConfiguration *config = [[WKWebViewConfiguration alloc] init];
config.allowsInlineMediaPlayback = YES;
config.mediaPlaybackRequiresUserAction = false;
_wkViewWeb = [[WKWebView alloc] initWithFrame:_viewWeb.frame config];
_wkViewWeb.scrollView.scrollEnabled = NO;
NSString *fullURL = @"file://.../TestSlide.html";
NSURL *url = [NSURL URLWithString:fullURL];
NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:10];

[_wkViewWeb loadRequest:request];

The html has the following function:

<SCRIPT Language="JavaScript">
function alertTest() {
    alert("Testing Alerts");
}
</SCRIPT>

And a button:

<b>Test Alerts: <input type="button" value="Alert Popup" onclick="alertTest()"><br></b> <br>

This setup works in UIWebView and in regular browsers, but does not work in WKWebView. Am I missing something in the configuration? Should I be using one of the WK delegates to control the alert/confirm dialog behavior? Thank you.

To solve this you need a WKUIDelegate for your web view. It is the duty of the delegate to decide if an alert should be displayed, and in what way. You need to implement this for alert, confirm and text input (prompt).

Here is sample code without any validation of the page url or security features:

- (void)webView:(WKWebView *)webView runJavaScriptAlertPanelWithMessage:(NSString *)message initiatedByFrame:(WKFrameInfo *)frame completionHandler:(void (^)(void))completionHandler
{
    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:message
                                                                             message:nil
                                                                      preferredStyle:UIAlertControllerStyleAlert];
    [alertController addAction:[UIAlertAction actionWithTitle:@"OK"
                                                        style:UIAlertActionStyleCancel
                                                      handler:^(UIAlertAction *action) {
                                                          completionHandler();
                                                      }]];
    [self presentViewController:alertController animated:YES completion:^{}];
}

More in the Official Documentation

Swift 3 with all 3 optional functions implemented:

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


func webView(_ webView: WKWebView, runJavaScriptConfirmPanelWithMessage message: String, initiatedByFrame frame: WKFrameInfo,
             completionHandler: @escaping (Bool) -> Void) {
    
    let alertController = UIAlertController(title: nil, message: message, preferredStyle: .actionSheet)
    
    alertController.addAction(UIAlertAction(title: "OK", style: .default, handler: { (action) in
        completionHandler(true)
    }))
    
    alertController.addAction(UIAlertAction(title: "Cancel", style: .default, handler: { (action) in
        completionHandler(false)
    }))
    
    present(alertController, animated: true, completion: nil)
}


func webView(_ webView: WKWebView, runJavaScriptTextInputPanelWithPrompt prompt: String, defaultText: String?, initiatedByFrame frame: WKFrameInfo,
             completionHandler: @escaping (String?) -> Void) {
    
    let alertController = UIAlertController(title: nil, message: prompt, preferredStyle: .actionSheet)
    
    alertController.addTextField { (textField) in
        textField.text = defaultText
    }
    
    alertController.addAction(UIAlertAction(title: "OK", style: .default, handler: { (action) in
        if let text = alertController.textFields?.first?.text {
            completionHandler(text)
        } else {
            completionHandler(defaultText)
        }
    }))
    
    alertController.addAction(UIAlertAction(title: "Cancel", style: .default, handler: { (action) in
        completionHandler(nil)
    }))
    
    present(alertController, animated: true, completion: nil)
}

Just to expand a bit, WKWebView requires you to show alerts, prompts, and confirms yourself. Do this by becoming a WKUIDelegate:

#import <WebKit/WebKit.h>
@interface MyController : UIViewController<WKUIDelegate>

Then assign the delegate:

web.UIDelegate = self;

Then you need to actually implement alert, prompt, and confirm. I create WKWebViewPanelManager.h/m as an easy implementation, so here's what I do:

- (void)webView:(WKWebView *)webView runJavaScriptAlertPanelWithMessage:(NSString *)message initiatedByFrame:(WKFrameInfo *)frame completionHandler:(void (^)(void))completionHandler {
    [WKWebViewPanelManager presentAlertOnController:self.view.window.rootViewController title:@"Alert" message:message handler:completionHandler];
}

- (void)webView:(WKWebView *)webView runJavaScriptConfirmPanelWithMessage:(NSString *)message initiatedByFrame:(WKFrameInfo *)frame completionHandler:(void (^)(BOOL result))completionHandler {
    [WKWebViewPanelManager presentConfirmOnController:self.view.window.rootViewController title:@"Confirm" message:message handler:completionHandler];
}

- (void)webView:(WKWebView *)webView runJavaScriptTextInputPanelWithPrompt:(NSString *)prompt defaultText:(nullable NSString *)defaultText initiatedByFrame:(WKFrameInfo *)frame completionHandler:(void (^)(NSString * __nullable result))completionHandler {
    [WKWebViewPanelManager presentPromptOnController:self.view.window.rootViewController title:@"Prompt" message:prompt defaultText:defaultText handler:completionHandler];
}

Of course, it's up to you to filter out bad alert/confirm/prompt requests.

And here's that in [tag:swift]:

func webView(webView: WKWebView, runJavaScriptAlertPanelWithMessage message: String,
             initiatedByFrame frame: WKFrameInfo, completionHandler: @escaping () -> Void) {
    
    let alertController = UIAlertController(title: message,
                                            message: nil,
                                            preferredStyle: .alert)
    
    alertController.addAction(UIAlertAction(title: "OK", style: .cancel) {
        _ in completionHandler()}
    )
    
    self.present(alertController, animated: true, completion: nil)
}

1. Implement the protocol to your WKWebview container controller. WKUIDelegate

2. Add preference to WKWebview to enable javascript in viewDidLoad() as.

   // enable JS
   webView.configuration.preferences.javaScriptEnabled = true
   

3. Register WKWebview UI Delegate in viewDidLoad() as

   self.webView.uiDelegate = self
   

4. Implement the below delegate in your class.

   func webView(_ webView: WKWebView, runJavaScriptAlertPanelWithMessage message: 
   String, initiatedByFrame frame: WKFrameInfo, completionHandler: @escaping () -> 
   Void) {
   let alertController = UIAlertController(title: message,message: nil,preferredStyle: 
   .alert)
   
   alertController.addAction(UIAlertAction(title: "OK", style: .cancel) {_ in 
   completionHandler()})
   
   self.present(alertController, animated: true, completion: nil)
   }
   

Here is the code in Swift 4.2

func webView(_ webView: WKWebView, runJavaScriptAlertPanelWithMessage message: String,
             initiatedByFrame frame: WKFrameInfo, completionHandler: @escaping () -> Void) {
    
    let alertController = UIAlertController(title: message, message: nil,
                                            preferredStyle: UIAlertController.Style.alert);
    
    alertController.addAction(UIAlertAction(title: "OK", style: UIAlertAction.Style.cancel) {
        _ in completionHandler()}
    );
    
    self.present(alertController, animated: true, completion: {});
}