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

@interface UIWebView (JavaScriptAlert) 
- (void)webView:(UIWebView *)sender runJavaScriptAlertPanelWithMessage:(NSString *)message initiatedByFrame:(WebFrame *)frame;
- (BOOL)webView:(UIWebView *)sender runJavaScriptConfirmPanelWithMessage:(NSString *)message initiatedByFrame:(WebFrame *)frame;
@end

@implementation UIWebView (JavaScriptAlert)
- (void)webView:(UIWebView *)sender runJavaScriptAlertPanelWithMessage:(NSString *)message initiatedByFrame:(WebFrame *)frame {
/*
UIAlertView* dialogue = [[UIAlertView alloc] initWithTitle:nil message:message delegate:nil cancelButtonTitle:@"好" otherButtonTitles:nil];
[dialogue show];
[dialogue autorelease];
*/
}
- (BOOL)webView:(UIWebView *)sender runJavaScriptConfirmPanelWithMessage:(NSString *)message initiatedByFrame:(WebFrame *)frame{
return NO;
}
@end