launchURL function
Implementation
Future<void> launchURL(String url, {LaunchMode mode = LaunchMode.platformDefault}) async {
final Uri url0 = Uri.parse(url);
if (await canLaunchUrl(url0)) {
launchUrl(url0, mode: mode);
} else {
// can't launch url, there is some error
throw "Could not launch $url";
}
}