How to block Javascript alert|confirm|promt in UIWebView before render completed?
ios, javascript, objective-c, uiwebview
Solution
After experimenting a bit with the suggested solutions regarding injecting a Javascript I fell back on the native platform.
Since a `UIWebView` translates all Javascript alerts into native `UIAlertViews` it is fairly simple to block it on the native end. Looking into `UIAlertView.h` there is only one public method for showing an alert which is conveniently called: `- (void)show;`.
This method can easily be either overridden in a subclass or through a category. I ended up using a category since the documentation mentions a warning for subclassing `UIAlertView`.
@interface UIAlertView (Blocker)
@end
#import "UIAlertView+Blocker.h"
@implementation UIAlertView (Blocker)
- (void)show {
return;
}
@end
Importing this category in the view controller that holds the `UIWebView` will block all instances of `UIAlertView` and in turn also all JS alerts.
I find this solution more robust since it does not rely on injecting Javascripts, changing HTML or using a third party library. It is also unrelated to timing (the JS-alert code can be in the header, body or in some third party lib).
Problem
There are multiple questions on SO already addressing similar issues but none answers my exact type of question. Most of the answers involves running a JS snippet and overloading the alert method as such: `window.alert = function() {};` The problem I am having is that the webpage loaded (which I have no control over the content) opens an alert before the rendering of the whole page completes. Because of this I cannot use the: `- (void)webViewDidFinishLoad:(UIWebView *)webView` delegate method to run the JS snippet. In addition running the same snippet in `- (void)webViewDidStartLoad:(UIWebView *)webView` won't do me any good since it executes before the DOM is loaded. Similar questions: - Capture (and prevent) alert() modal in UIWebView - Can I handle alert inside UIWebViewDelegate? - UIWebView: Can I disable the javascript alert() inside any web page? Any pointers on this?