TypeScript:

How to type a talk

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Heitor Ramon

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Agenda

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Migration Stories 

AirBnb: Brie Bunge at Airbnb gave a talk at JSConf Hawaiʻi on how Airbnb adopted TypeScript at Scale

 

(https://www.youtube.com/watch?v=P-J9Eg7hJwE)

Google: Rodoslav Kirov and Bowen Ni covered how TypeScript became one of the five languages available at Google at TSConf 2018

 

(https://www.youtube.com/watch?v=sjov1k5jexA)

Slack: Felix Rieseberg at Slack covered the transition of their desktop app from JavaScript to TypeScript in their blog

 

(https://slack.engineering/typescript-at-slack/)

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Who use it?

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Why
Types are
Fundamental

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Pros and Cons of using it

Do I need to say anything more?

Pros

  • Maintainability
  • Refactor
  • Easy reading and understanding
  • @types and .d.ts

Cons

  • It's not truly typed
  • Adds a new layer of complexibility on JavaScript
  • Learning curve for newcomers

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Back to the Basic

In TypeScript, there are some basic types that are used by the variables and return types.

Those types are:

  • String
  • Number
  • Boolean
  • Array
  • Unknown
  • Enum
  • Any 
  • Void
  • Object

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Interfaces

Using interfaces in Typescript is a good way to create a contract between classes, objects, or even complex types.

 

An interface can be manipulated and extended to reach its final form.

interface Shape {
  area: number;
}

interface Square extends Shape {
  width: number;
  height?: number;
}

interface Circle extends Share {
  radius: number;
}

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Custom Types

With custom, types bring the possibility to create new frontiers to the code, where you can bring to the game new comments that are not implemented in the core compiler and re-use codes.

 

Custom types can be inferred from new types, interfaces, mixed of new methods or special joiners.

type RetroGames = 'Atari' | 'Pong' | 'Commodore';

type EightBitConsole = 'Famicon' | 'MasterSystem';

type VideoGame = RetroGames | EightBitConsole;

interface Shape { 
  area: number;
}

interface Square extends Shape {
  width: number;
  height?: number;
}

interface Circle extends Shape {
  radius: number;
}
  
type GeometricForm = Square | Circle

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Advanced Types

TypeScript provides some advanced types that can improve the code, where you can take advantage within as a type guard or as a new type on the compiler.

 

The type guards provide security on compiling and development.

const pet = getSmallPet();
const fishPet = pet as Fish;
const birdPet = pet as Bird;

if (fishPet.swim) {
  fishPet.swim();
} else if (birdPet.fly) {
  birdPet.fly();
}

function f<T extends boolean>(x: T): T extends true 
? string 
: number;

function foo(x: string | number): string | number;

type T1 = ReturnType<typeof foo>;

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Utility Types

TypeScript provides some utility types with helper interfaces that use Generics to get the types and interfaces.

 

Those helpers can be imported into the code and used everywhere you could use an interface or a type.

interface Todo {
  title: string;
  description: string;
  completed?: boolean;
}

function updateTodo(fieldsToUpdate: Partial<Todo>) {
  return { ...todo, ...fieldsToUpdate };
}

type TodoPreview = Omit<Todo, "description">;

const todo: TodoPreview = {
  title: "Clean room",
  completed: false,
};

const todo2: Required<Todo> = { 
  title: "Clean House",
  description: "Clear the House",
  completed: true,
};

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Decorators

With ES6 bringing classes and the possibility to create an annotation and modifying classes.

 

A Decorator can be attached to a class declaration, method, accessor, property, or parameter.

function f() {
  console.log("f(): evaluated");
  return function () {
    console.log("f(): called");
  };
}

function g() {
  console.log("g(): evaluated");
  return function (
    target,
    propertyKey: string,
    descriptor: PropertyDescriptor
  ) {
    console.log("g(): called");
  };
}

class C {
  @f()
  @g()
  method() {}
}

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Iterators and Generators

JavaScript with its new versions brought the possibility of Generators functions.

 

Those functions can be exited and later re-entered. Their context (variable bindings) will be saved across re-entrances. 

 

Iterators are functions that define a sequence and potentially a return value upon its termination. 

function* generator(i) {
  yield i;
  yield i + 10;
}

const gen = generator(10);

console.log(gen.next().value); // 10

console.log(gen.next().value); // 20

const it = makeRangeIterator(1, 10, 2);

let result = it.next();
while (!result.done) {
 console.log(result.value); // 1 3 5 7 9
 result = it.next();
}

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Where I can learn?

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Thank You

Typescript: How to type a talk

By Heitor Ramon Ribeiro

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Typescript: How to type a talk

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