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

Question

Since dart version 2.6, dart supports extensions:

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

So you can just call your extension like this:

import "string_extension.dart";

var someCapitalizedString = "someString".capitalize();

Copy this somewhere:

extension StringCasingExtension on String {
  String toCapitalized() => length > 0 ?'${this[0].toUpperCase()}${substring(1)}':'';
  String toTitleCase() => replaceAll(RegExp(' +'), ' ').split(' ').map((str) => str.toCapitalized()).join(' ');
}

Usage:

// import StringCasingExtension

final helloWorld = 'hello world'.toCapitalized(); // 'Hello world'
final helloWorld = 'hello world'.toUpperCase(); // 'HELLO WORLD'
final helloWorldCap = 'hello world'.toTitleCase(); // 'Hello World'

Substring parsing in the other answers do not account for locale variances. The toBeginningOfSentenceCase() function in the intl/intl.dart package handles basic sentence-casing and the dotted "i" in Turkish and Azeri.

import 'package:intl/intl.dart';
...
String sentence = toBeginningOfSentenceCase('this is a string'); // This is a string

void main() {
  print(capitalize("this is a string"));
  // displays "This is a string"
}

String capitalize(String s) => s[0].toUpperCase() + s.substring(1);

See this snippet running on DartPad : https://dartpad.dartlang.org/c8ffb8995abe259e9643

Alternatively you can use the strings package, see capitalize.