The best approach you can use, is to resize the main view, specially if your application uses a footer.
on MainViewController.m using the viewDidLoad method, after [super viewDidLoad];
NSArray *vComp = [[UIDevice currentDevice].systemVersion componentsSeparatedByString:@"."];
if ([[vComp objectAtIndex:0] intValue] >= 7) {
// iOS 7 or above
CGRect oldBounds = [self.view bounds];
CGRect newViewBounds = CGRectMake( 0, -10, oldBounds.size.width, oldBounds.size.height-20 );
CGRect newWebViewBounds = CGRectMake( 0, -20, oldBounds.size.width, oldBounds.size.height-40 );
[self.view setBounds:newViewBounds];
[self.webView setBounds:newWebViewBounds];
}
then you won't need to modify any javascript into your application