How can my iPhone Objective-C code get notified of Javascript errors in a UIWebView?

Question

I need to have my iPhone Objective-C code catch Javascript errors in a UIWebView. That includes uncaught exceptions, syntax errors when loading files, undefined variable re

Answer 1

I have now found one way using the script debugger hooks in WebView (note, NOT UIWebView). I first had to subclass UIWebView and add a method like this:

- (void)webView:(id)webView windowScriptObjectAvailable:(id)newWindowScriptObject {
    // save these goodies
    windowScriptObject = newWindowScriptObject;
    privateWebView = webView;

    if (scriptDebuggingEnabled) {
        [webView setScriptDebugDelegate:[[YourScriptDebugDelegate alloc] init]];
    }
}

Next you should create a YourScriptDebugDelegate class that contains methods like these:

// in YourScriptDebugDelegate

- (void)webView:(WebView *)webView       didParseSource:(NSString *)source
 baseLineNumber:(unsigned)lineNumber
        fromURL:(NSURL *)url
       sourceId:(int)sid
    forWebFrame:(WebFrame *)webFrame
{
    NSLog(@"NSDD: called didParseSource: sid=%d, url=%@", sid, url);
}

// some source failed to parse
- (void)webView:(WebView *)webView  failedToParseSource:(NSString *)source
 baseLineNumber:(unsigned)lineNumber
        fromURL:(NSURL *)url
      withError:(NSError *)error
    forWebFrame:(WebFrame *)webFrame
{
    NSLog(@"NSDD: called failedToParseSource: url=%@ line=%d error=%@\nsource=%@", url, lineNumber, error, source);
}

- (void)webView:(WebView *)webView   exceptionWasRaised:(WebScriptCallFrame *)frame
       sourceId:(int)sid
           line:(int)lineno
    forWebFrame:(WebFrame *)webFrame
{
    NSLog(@"NSDD: exception: sid=%d line=%d function=%@, caller=%@, exception=%@", 
          sid, lineno, [frame functionName], [frame caller], [frame exception]);
}

There is probably a large runtime impact for this, as the debug delegate can also supply methods to be called for entering and exiting a stack frame, and for executing each line of code.

See http://www.koders.com/noncode/fid7DE7ECEB052C3531743728D41A233A951C79E0AE.aspx for the Objective-C++ definition of WebScriptDebugDelegate.

Those other methods:

// just entered a stack frame (i.e. called a function, or started global scope)
- (void)webView:(WebView *)webView    didEnterCallFrame:(WebScriptCallFrame *)frame
      sourceId:(int)sid
          line:(int)lineno
   forWebFrame:(WebFrame *)webFrame;

// about to execute some code
- (void)webView:(WebView *)webView willExecuteStatement:(WebScriptCallFrame *)frame
      sourceId:(int)sid
          line:(int)lineno
   forWebFrame:(WebFrame *)webFrame;

// about to leave a stack frame (i.e. return from a function)
- (void)webView:(WebView *)webView   willLeaveCallFrame:(WebScriptCallFrame *)frame
      sourceId:(int)sid
          line:(int)lineno
   forWebFrame:(WebFrame *)webFrame;

Note that this is all hidden away in a private framework, so don't try to put this in code you submit to the App Store, and be prepared for some hackery to get it to work.

Answer 2

I created a nice little drop-in category that you can add to your project... It is based on Robert Sanders solution. Kudos.

You can dowload it here:

UIWebView+Debug

This should make it a lot easier to debug you UIWebView :)

Answer 3

One way that works during development if you have Safari v 6+ (I'm uncertain what iOS version you need) is to use the Safari development tools and hook into the UIWebView through it.

1. In Safari: Enable the Develop Menu (Preferences > Advanced > Show Develop menu in menu bar)
2. Plug your phone into the computer via the cable.
3. List item
4. Load up the app (either through xcode or just launch it) and go to the screen you want to debug.
5. Back in Safari, open the Develop menu, look for the name of your device in that menu (mine is called iPhone 5), should be right under User Agent.
6. Select it and you should see a drop down of the web views currently visible in your app.
7. If you have more than one webview on the screen you can try to tell them apart by rolling over the name of the app in the develop menu. The corresponding UIWebView will turn blue.
8. Select the name of the app, the develop window opens and you can inspect the console. You can even issue JS commands through it.

Answer 4

I used the great solution proposed from Robert Sanders: How can my iPhone Objective-C code get notified of Javascript errors in a UIWebView?

That hook for webkit works fine also on iPhone. Instead of standard UIWebView I allocated derived MyUIWebView. I needed also to define hidden classes inside MyWebScriptObjectDelegate.h:

@class WebView;
@class WebFrame;
@class WebScriptCallFrame;

Within the ios sdk 4.1 the function:

- (void)webView:(id)webView windowScriptObjectAvailable:(id)newWindowScriptObject 

is deprecated and instead of it I used the function:

- (void)webView:(id)sender didClearWindowObject:(id)windowObject forFrame:(WebFrame*)frame

Also, I get some annoying warnings like "NSObject may not respond -windowScriptObject" because the class interface is hidden. I ignore them and it works nice.

Answer 5

I have created an SDK kosher error reporter that includes:

1. The error message
2. The name of the file the error happens in
3. The line number the error happens on
4. The JavaScript callstack including parameters passed

It is part of the QuickConnectiPhone framework available from the sourceForge project

There is even an example application that shows how to send an error message to the Xcode terminal.

All you need to do is to surround your JavaScript code, including function definitions, etc. with try catch. It should look like this.

try{
//put your code here
}
catch(err){
    logError(err);
}

It doesn't work really well with compilation errors but works with all others. Even anonymous functions.

The development blog is here is here and includes links to the wiki, sourceForge, the google group, and twitter. Maybe this would help you out.

Answer 6

I have done this in firmware 1.x but not 2.x. Here is the code I used in 1.x, it should at least help you on your way.

// Dismiss Javascript alerts and telephone confirms
/*- (void)alertSheet:(UIAlertSheet*)sheet buttonClicked:(int)button
{
    if (button == 1)
    {
        [sheet setContext: nil];
    }

    [sheet dismiss];
}*/

// Javascript errors and logs
- (void) webView: (WebView*)webView addMessageToConsole: (NSDictionary*)dictionary
{
    NSLog(@"Javascript log: %@", dictionary);
}

// Javascript alerts
- (void) webView: (WebView*)webView runJavaScriptAlertPanelWithMessage: (NSString*) message initiatedByFrame: (WebFrame*) frame
{
    NSLog(@"Javascript Alert: %@", message);

    UIAlertSheet *alertSheet = [[UIAlertSheet alloc] init];
    [alertSheet setTitle: @"Javascript Alert"];
    [alertSheet addButtonWithTitle: @"OK"];
    [alertSheet setBodyText:message];
    [alertSheet setDelegate: self];
    [alertSheet setContext: self];
    [alertSheet popupAlertAnimated:YES];
}