All Aboard the Type Train

Kadi Kraman

@kadikraman

πŸš‚

Hi, my name is

Kadi

I work at

ormidable

... and I write a lot of JavaScript

@kadikraman

@kadikraman

@kadikraman

πŸš‚

πŸšƒ

πŸšƒ

πŸšƒ

Flow

TypeScript

Since PEP 484

PHP 7.4

@kadikraman

But why?

Frontend

Backend

@kadikraman

"The Stack"

Frontend

Backend

πŸ‘‘

@kadikraman

"The Stack"

Frontend

Backend

πŸ‘‘

@kadikraman

@kadikraman

Let's talk about JavaScript

@kadikraman

function addOne(array) {
  return array.map(val => val + 1);
}

  addOne([1, 2, 3])

// [2, 3, 4]


  addOne({})

@kadikraman

function addOne(array) {
  return array.map(val => val + 1);
}
 /**
  * Adds 1 to each element in the array
  * @param array (array of numbers): array to increment
  */
function addOne(array) {
  return array.map(val => val + 1);
}

@kadikraman

I could add comments?

Just kidding - no one reads comments

function addOne(array) {
  if (!Array.isArray(array) || !array.every(val => typeof val === "number")) {
    return [];
  }
    
  return array.map(val => val + 1);
}

@kadikraman

I could add a fallback?

But this function is only meant to be used on a number array

function addOne(array: number[]): number[] {
  return array.map(val => val + 1);
}

@kadikraman

... or I could add explicit type information?

* not valid in plain JavaScript

@kadikraman

⚑️News Flash!⚑️

@kadikraman

All programming languages have a type system

The difference is when the type checking is done!

@kadikraman

Compile time

Run time

@kadikraman

Static vs Dynamic

Compile time vs run time type checking

Strong vs Weak

Typed vs Untyped

@kadikraman

Run time

πŸ€·β€β™€οΈ Β πŸ€·β€β™€οΈ Β πŸ€·β€β™€οΈ

Compile time

@kadikraman

Run time

Compile time

Type errors?Β 

Errors can still occur, but not type errors

@kadikraman

Static Typing - the downsides

@kadikraman

( source: https://xkcd.com/303/Β )

It takes time

@kadikraman

It adds verbosity

vs

function addOne(array: number[]): number[] {
  return array.map(val => val + 1);
}
function addOne(array) {
  return array.map(val => val + 1);
}

@kadikraman

Static Typing - the upsides

@kadikraman

Fewer runtime exceptions

(no type errors)

@kadikraman

Fewer tests

(you don't need to test for type correctness)

@kadikraman

Dynamic Typing - the upsides

@kadikraman

Faster

(no compile step)

@kadikraman

More Flexible

var myValue = 1;

myValue = "potato";

@kadikraman

Dynamic Typing - the downsides

@kadikraman

Runtime Type Errors

@kadikraman

Harder to Refactor with ConfidenceΒ 

🀞

@kadikraman

Dynamic

Static

βœ… Faster

βœ… More flexible

Β 

❌ Runtime type errors

❌ Harder to refactor

βœ… Fewer runtime exceptions

βœ… Fewer tests

Β 

❌ Takes longer

❌ Adds verbosity

Could we borrow concepts from statically typed languages?

@kadikraman

How to reduce Type Errors

in a Dynamically Typed language?

@kadikraman

ESLint for type checking in JavaScript

@kadikraman

React Community

2 years ago

Infers type information from existing code

@kadikraman

You can enforce types

@kadikraman

There's a community for typing node_modules

@kadikraman

@kadikraman

Downsides?

Configuration 😱

Memory πŸ’€

You can easily ignore it 😳

@kadikraman

React Community

now

@kadikraman

Static type checker

Language

@kadikraman

@kadikraman

You can still...

Infer type information from existing code

@kadikraman

You can still...

Enforce types

@kadikraman

The node_modules community is bigger

Flow

TypeScript

@kadikraman

Configuration

Flow 😱 

TypeScript βœ…

@kadikraman

Memory

Flow 😱 

TypeScript βœ…

@kadikraman

In summary...

βœ… has a larger community

βœ… has a faster release cycle

βœ… is more reliable

βœ… is easier to set up

βœ… has an ability to enforce type-checking

Β 

❌ although you can still ignore type checking

TypeScript...

But I don't want to use TypeScript!

@kadikraman

Do you even care about static type checking?

NO

YES

Use plain JavaScript!

@kadikraman

Why can't we just use a "proper" typed language?

@kadikraman

@kadikraman

Frontend

Backend

πŸ‘‘

@kadikraman

Frontend

Backend

ReasonML (2016 by Jordan Walke)

(Transpiles to OCaml which compiles to JS)


  let add = (x: int, y: int) : int => x + y;

@kadikraman

@kadikraman

type user = { firstName: string, lastName: string };

let user: user = {
  firstName: "Harper",
  lastName: "Perez"
};

let formatName user =>
  user.firstName ^ " " ^ user.lastName;

let hello =
  (ReactRe.stringToElement ("Hello, " ^ formatName user));

let header =
  <h1 title=(formatName user)>
    hello
  </h1>;

ReactDOMRe.renderToElementWithId header "root";

Elm (2012 by Evan Czaplicki)

  add : Number -> Number -> Number
  add a b =
    a + b

"no runtime exceptions"

(compiles to JS)

@kadikraman

import Browser
import Html exposing (Html, button, div, text)
import Html.Events exposing (onClick)

main =
  Browser.sandbox { init = 0, update = update, view = view }

type Msg = Increment | Decrement

update msg model =
  case msg of
    Increment ->
      model + 1

    Decrement ->
      model - 1

view model =
  div []
    [ button [ onClick Decrement ] [ text "-" ]
    , div [] [ text (String.fromInt model) ]
    , button [ onClick Increment ] [ text "+" ]
    ]

@kadikraman

@kadikraman

1996

2014

2016

2012

JavaScript

Elm

TypeScript

Flow

Reason

(3 years)

(5 years)

(7 years)

(23 years)

OCaml

2017

(4 years)

Web Assembly

New project, who dis?

Reliability in prod

Effort to learn

JavaScript

Flow

Reason

Elm

TypeScript

@kadikraman

New project, who dis?

Reliability in prod

Effort to learn

JavaScript

Flow

Reason

Elm

TypeScript

@kadikraman

Server Fetched Partials?

πŸ‘»

Add types to your code

Stay Safe

@kadikraman

For riding the Type Train πŸš‚

Thank you!

@kadikraman

All Aboard the Type Train (FSEU2019)

By Kadi Kraman

All Aboard the Type Train (FSEU2019)

JavaScript is a language of add-ons, and one of its more recent trends is typing. There are obvious benefits to typing, but what are the drawbacks? Should you choose Flow or TypeScript? Why use types at all? And why not just go straight to Reason?

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