The main() function

Every app must have a top-level main() function, which serves as theentrypoint to the app. The main() function returns void and has anoptional List<String> parameter for arguments.

Here’s an example of the main() function for a web app:

void main() {
  querySelector('#sample_text_id')
    ..text = 'Click me!'
    ..onClick.listen(reverseText);
}

Note: The .. syntax in the preceding code is called a cascade. With cascades, you can perform multiple operations on the members of a single object.

Here’s an example of the main() function for a command-line app thattakes arguments:

// Run the app like this: dart args.dart 1 test
void main(List<String> arguments) {
  print(arguments);
  assert(arguments.length == 2);
  assert(int.parse(arguments[0]) == 1);
  assert(arguments[1] == 'test');
}

You can use the args library todefine and parse command-line arguments.