converting-ts-to-dart

TypeScript to Dart 3 Conversion Guide

Goal

Provide clear, idiomatic mappings from TypeScript syntax and patterns to modern Dart 3 equivalents. Every conversion should produce code that feels native to Dart — not a line-by-line transliteration.

Instructions

1. Type System Mapping

1.1 Primitive Types

TypeScript and Dart share similar primitives but with different names.

// TypeScript
let name: string = "Zack";
let age: number = 25;
let active: boolean = true;
let items: string[] = ["a", "b"];
let pair: [string, number] = ["age", 25];

// Dart 3
final name = 'Zack';
final age = 25;
final active = true;
final items = ['a', 'b'];
final pair = ('age', 25); // Record instead of Tuple

Key mappings:

TypeScript	Dart
string	String
number	int / double / num
boolean	bool
any	dynamic (avoid when possible)
unknown	Object?
void	void
null / undefined	null (Dart has no undefined)
never	Never
T[] / Array<T>	List<T>
[A, B] (Tuple)	(A, B) (Record)
Record<K, V> / { [key: string]: V }	Map<K, V>
Set<T>	Set<T>
Promise<T>	Future<T>
Observable<T>	Stream<T>

1.2 Union Types

Dart has no direct union type. Convert using sealed classes for complex cases, or Object + pattern matching for simple ones.

// TypeScript
type Result = Success | Failure;
type StringOrNum = string | number;

// Dart 3 — sealed class for ADTs
sealed class Result {}
class Success extends Result { final String data; Success(this.data); }
class Failure extends Result { final String error; Failure(this.error); }

// Simple union — use pattern matching
void process(Object value) {
  switch (value) {
    case String s: print('String: $s');
    case int n:    print('Int: $n');
  }
}

1.3 Literal Types and Enums

// TypeScript
type Direction = "up" | "down" | "left" | "right";
enum Status { Active = "ACTIVE", Inactive = "INACTIVE" }

// Dart 3 — enhanced enum
enum Direction { up, down, left, right }
enum Status {
  active('ACTIVE'),
  inactive('INACTIVE');
  final String value;
  const Status(this.value);
}