How to capitalize the first letter of a string in dart?

Since dart version 2.6, dart supports extensions:

extension StringExtension on String {
    String capitalize() {
      return "${this[0].toUpperCase()}${this.substring(1).toLowerCase()}";
    }
}

So you can just call your extension like this:

import "string_extension.dart";

var someCapitalizedString = "someString".capitalize();