Intercept "location.href" in a UIWebView, Objective-C

Question

What is the correct code to intercept location.href URL in a UIWebView?

- (NSString*)actionURL
{       
    NSString *script = @"document.getElementById('action_url').name";
    return [webView stringByEvaluatingJavaScriptFromString:script];     
}

This code doesn't work :(