What are some methods to debug Javascript inside of a UIWebView?

Question

I'm trying to figure out why something with Javascript isn't working inside of a UIWebView. To my knowledge, there is no way to set a breakpoint inside of XCode for a js file. No problemo, I'll just go back to 2004 and use alert statemen-- oh wait they don't seem to work inside of a UIWebView either!

The only thing I could think of is by exporting my HTML And JS files to my desktop and then just doing my debugging inside of Safari. And that works! But of course, the bug I'm fighting with in the UIWebView doesn't occur in Safari.

Are there any other ways for debugging inside of a UIWebView, or any tricks that I can use akin to using the old-school alert method?

Answer 1

alert() certainly works for me.

However, you can also do lots of other things, like make your own DHTML alert that pops up in a layer. This can be nice because you can do multiple alerts to a single div, without stopping your app. You should also be able to write a stack trace to it (the stack trace is in the exception object, and you can always throw your own exceptions).

Alternatively, if running on the simulator your custom "alert()" could call into objective C, and display the string in the iPhone simulator's console window:

document.location.href = "http://debugger/" + 
   encodeURIComponent(outputString);   

and on the objective C side:

//--------------------------------------------------------------------
- (BOOL)webView:(UIWebView*)webView 
       shouldStartLoadWithRequest: (NSURLRequest*)req 
       navigationType:(UIWebViewNavigationType)navigationType {
    if ([[[req URL] host] isEqualToString:@"debugger"]){
        // do stuff with [[req URL] path] 
       }
}

That said, I have an app that is heavy on the UiWebView / javascript stuff, and I tend to do most javascript dev in Chrome (simulating what is necessary from the iPhone environment)

Answer 2

You can set up a system like that used in PhoneGap to send messages from JavaScript to Objective-C and log from there. In a nutshell, they are setting document.location with a custom scheme and blocking that scheme in the delegate callback.

You can take advantage of the fact that a UIWebView is most of the delegates for a WebView. WebKit is technically undocumented for iPhone, but mostly the same as specified in the desktop WebKit headers, possibly including the WebScriptObject. I use this for debugging, but be sure to strip this code out before submitting to Apple.

To get a WebView from a UIWebView, implement a delegate method like -(void) webView:(id)inWebView didFinishLoadForFrame:(id)inWebFrame in a subclass of UIWebView. Call super if you use that one.