Teams App Developer

ruby-to-ts-ts

purpose

Rewriting Ruby source code as idiomatic TypeScript — mapping Ruby language constructs, OOP patterns, metaprogramming, and common idioms to their TypeScript equivalents.

rules

1. Ruby blocks (do...end / { |x| }) map to arrow functions. array.each { |item| puts item } becomes array.forEach((item) => console.log(item)). Ruby's yield inside methods maps to calling a callback parameter.

2. Ruby mixins (include Module) map to TypeScript interfaces + composition. Do NOT use class inheritance to simulate mixins — use interface implementation with helper functions or the mixin pattern (applyMixins).

3. Ruby duck typing maps to TypeScript structural typing. If Ruby code checks obj.respond_to?(:method), define an interface with that method and use a type guard: function hasMethod(obj: unknown): obj is HasMethod.

4. Ruby attr_accessor :name maps to a class property with TypeScript accessor shorthand: constructor(public name: string) {} or explicit get/set pairs if logic is needed.

5. Ruby symbols (:name) map to string literal types or enum members. A method accepting type: :admin | :user becomes type: 'admin' | 'user' in TypeScript.

6. Ruby hashes ({ key: value }) map to TypeScript objects or Record<string, T>. Named-parameter hashes (def method(opts = {})) become destructured typed parameters: function method({ key1, key2 }: Options).

7. Ruby nil maps to null or undefined. Use null for explicit absence and undefined for optional/missing. Ruby's &. safe navigator maps to optional chaining (?.).

8. Ruby begin/rescue/ensure maps to try/catch/finally. Ruby's typed rescue (rescue TypeError => e) maps to catching and narrowing: catch (e) { if (e instanceof TypeError) ... }.

9. Ruby open classes and monkey-patching have NO TypeScript equivalent. Redesign as wrapper functions, decorator patterns, or module augmentation (declare module for extending third-party types).

10. Ruby metaprogramming (define_method, method_missing, send) has no direct equivalent. Replace define_method loops with computed property patterns or factory functions. Replace method_missing with Proxy objects (sparingly) or explicit handler maps.

11. Ruby's Enumerable methods map to JavaScript array methods: map→map, select→filter, reject→filter (inverted), reduce→reduce, detect/find→find, flat_map→flatMap, each_with_object→reduce, group_by→custom groupBy or Object.groupBy().

12. Ruby string interpolation "Hello #{name}" maps to template literals `Hello ${name}`.

13. Ruby Proc.new / lambda / -> all map to arrow functions. Ruby's distinction between procs and lambdas (arity checking, return behavior) disappears — TypeScript arrow functions always behave like Ruby lambdas.

14. Ruby modules used as namespaces map to TypeScript modules (files) with named exports. Do NOT use TypeScript namespace keyword — use ES module export instead.

patterns

Ruby class with mixins → TypeScript interface + composition

# --- Before (Ruby) ---
module Greetable
  def greet
    "Hello, I'm #{name}"
  end
end

module Trackable
  def track(event)
    puts "Tracking #{event} for #{name}"
  end
end

class User
  include Greetable
  include Trackable

  attr_accessor :name, :email

  def initialize(name, email)
    @name = name
    @email = email
  end
end

user = User.new("Alice", "[email protected]")
puts user.greet
user.track("login")

// --- After (TypeScript) ---
interface Greetable {
  name: string;
  greet(): string;
}

function greetMixin<T extends { name: string }>(obj: T): T & Greetable {
  return Object.assign(obj, {
    greet() {
      return `Hello, I'm ${obj.name}`;
    },
  });
}

interface Trackable {
  name: string;
  track(event: string): void;
}

function trackMixin<T extends { name: string }>(obj: T): T & Trackable {
  return Object.assign(obj, {
    track(event: string) {
      console.log(`Tracking ${event} for ${obj.name}`);
    },
  });
}

class User {
  constructor(
    public name: string,
    public email: string,
  ) {}
}

// Apply mixins
function createUser(name: string, email: string): User & Greetable & Trackable {
  const user = new User(name, email);
  return trackMixin(greetMixin(user));
}

const user = createUser("Alice", "[email protected]");
console.log(user.greet());
user.track("login");

Ruby hash options / keyword args → TypeScript typed parameters

# --- Before (Ruby) ---
class SlackNotifier
  def initialize(opts = {})
    @webhook_url = opts[:webhook_url] || ENV['SLACK_WEBHOOK']
    @channel = opts[:channel] || '#general'
    @username = opts[:username] || 'bot'
  end

  def notify(message, opts = {})
    icon = opts.fetch(:icon_emoji, ':robot_face:')
    thread_ts = opts[:thread_ts]
    # ... send notification
  end
end

notifier = SlackNotifier.new(webhook_url: 'https://...', channel: '#alerts')
notifier.notify('Deploy complete', icon_emoji: ':rocket:')

// --- After (TypeScript) ---
interface SlackNotifierOptions {
  webhookUrl?: string;
  channel?: string;
  username?: string;
}

interface NotifyOptions {
  iconEmoji?: string;
  threadTs?: string;
}

class SlackNotifier {
  private readonly webhookUrl: string;
  private readonly channel: string;
  private readonly username: string;

  constructor({
    webhookUrl = process.env.SLACK_WEBHOOK ?? '',
    channel = '#general',
    username = 'bot',
  }: SlackNotifierOptions = {}) {
    this.webhookUrl = webhookUrl;
    this.channel = channel;
    this.username = username;
  }

  notify(message: string, { iconEmoji = ':robot_face:', threadTs }: NotifyOptions = {}): void {
    // ... send notification
  }
}

const notifier = new SlackNotifier({ webhookUrl: 'https://...', channel: '#alerts' });
notifier.notify('Deploy complete', { iconEmoji: ':rocket:' });

Ruby Enumerable → TypeScript array methods

# --- Before (Ruby) ---
users = get_users()
active_admins = users
  .select { |u| u.active? }
  .reject { |u| u.guest? }
  .select { |u| u.role == :admin }
  .map { |u| { name: u.name, email: u.email } }
  .sort_by { |h| h[:name] }

// --- After (TypeScript) ---
interface User {
  name: string;
  email: string;
  active: boolean;
  guest: boolean;
  role: 'admin' | 'user' | 'guest';
}

const users: User[] = getUsers();
const activeAdmins = users
  .filter((u) => u.active)
  .filter((u) => !u.guest)
  .filter((u) => u.role === 'admin')
  .map((u) => ({ name: u.name, email: u.email }))
  .sort((a, b) => a.name.localeCompare(b.name));

pitfalls

• Ruby truthiness vs JS truthiness: In Ruby, only nil and false are falsy. In JS/TS, 0, "", NaN, null, undefined, and false are all falsy. Ruby code like if count (truthy when 0) must become if (count !== null && count !== undefined) in TS.

• Ruby == is value equality; JS === is identity for objects: Ruby == on strings/numbers compares values. TS === on primitives works the same, but on objects it compares references. Deep equality requires a library or custom check.

• each return value: Ruby's each returns the original array. JS forEach returns undefined. Don't chain after forEach.

• Ruby ranges (1..10): No TS equivalent. Use Array.from({ length: 10 }, (_, i) => i + 1) or a simple for loop.

• String is mutable in Ruby, immutable in JS: Ruby str.gsub! mutates in place. TS strings are immutable — always reassign: str = str.replace(...).

• Ruby exception hierarchy: Ruby has StandardError, RuntimeError, etc. TS/JS only has Error. Use custom error classes extending Error if you need a hierarchy.

• Snake_case to camelCase: Ruby uses snake_case for methods/variables. TypeScript convention is camelCase. Convert all identifiers, but keep API payloads in their original format (e.g., Slack payloads use snake_case).

• Ruby require is file-level, not scoped: All Ruby require statements load globally. TS import is scoped to the file. This means Ruby's implicit global availability must become explicit imports in every file that uses the dependency.

• Sinatra/Rack → Express: Ruby Sinatra routes (get '/' do ... end) map to Express (app.get('/', (req, res) => { ... })). The middleware patterns are similar but request/response APIs differ completely.

references

• https://www.typescriptlang.org/docs/handbook/2/classes.html -- TS classes

• https://www.typescriptlang.org/docs/handbook/2/objects.html -- structural typing

• https://www.typescriptlang.org/docs/handbook/mixins.html -- mixin pattern

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array -- JS array methods (Enumerable equivalents)

• https://ruby-doc.org/core/Enumerable.html -- Ruby Enumerable reference (for mapping)

instructions

Use this expert when rewriting Ruby source code in TypeScript. Start by identifying the Ruby constructs in use (classes, modules/mixins, blocks, metaprogramming, Enumerable chains) and map each to its TS equivalent using the rules above. Pay special attention to truthiness differences, mixin patterns, and naming convention changes (snake_case → camelCase). Pair with dependency-mapping-ts.md for gem → npm package equivalents, and type-mapping-ts.md for cross-language type reference.

research

Deep Research prompt:

"Write a micro expert on converting Ruby to TypeScript. Cover: blocks to arrow functions, mixins to interfaces/composition, duck typing to structural typing, attr_accessor to class properties, symbol to string literals, hash options to typed parameters, metaprogramming alternatives, Enumerable methods to array methods, exception handling, truthiness differences, and naming convention conversion (snake_case to camelCase). Include 3 worked examples."