UIWebView: Can I disable the javascript alert() inside any web page?

Add this after your web view has loaded its content

[MyWebView stringByEvaluatingJavaScriptFromString:@"window.alert=null;"];

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;.

@interface UIAlertView (Blocker)
@end

#import "UIAlertView+Blocker.h"

@implementation UIAlertView (Blocker)

- (void)show {
   return;
}
@end

You can find the answer here: https://stackoverflow.com/a/21698251/2377378

You can bind window.alert to another function. So:

window.alert = function() {
  //does nothing so effectively "disables" alert
};

Make sure you do this before you call any alerts. The neat thing about this is you can customize the way you display messages to the user. So you could override window.alert to log to the console (for debugging purposes) or you can render it on the page (with a lightbox or something similar).