JavaScript for Swift Developers

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JAVASCRIPT for Swift Developers

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SWIFT let dog = Dog(age: 3, furColor: "brown") print(dog) // => "Dog(age: 3)"

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JAVASCRIPT let dog = new Dog(3, "brown"); console.log(dog); // => "Dog(age: 3)"

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SUPERFICIAL

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▸ Both have variable declarations with let. ▸ Swift has parameter names. ▸ Different calls to make console prints. ▸ JavaScript has a new operator. ▸ JavaScript has semicolons.

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VARIABLE DECLARATIONS ▸ var ▸ let ▸ const

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var ▸ In Swift: declares a mutable variable ▸ In JavaScript: declares a variable which is hoisted within the function or global scope

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let ▸ In Swift: declares an immutable variable, enforced beyond re-assignments for value types ▸ In JavaScript: declares a variable which is block-scoped

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const ▸ Only in JavaScript: declares a variable which is block-scoped and not re-assignable

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;

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WRITE MULTIPLE STATEMENTS IN A SINGLE LINE

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IN SWIFT IT'S OPTIONAL.

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IN JAVASCRIPT IT'S SOMETIMES OPTIONAL.

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AUTOMATIC SEMICOLON INSERTION

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return { name: "This is fine." };

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return; { name: "This is fine." };

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semi: ["error", "always"] // or: ["error", "never"]

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BUT THERE IS MORE THAN THE SUPERFICIAL…

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STEP BACK What do we compare?

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SWIFT ▸ 2014: 1.0 ▸ … ▸ 2017-03-27: 3.1

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JAVASCRIPT ▸ 1996: 1.0 ▸ 2000: 1.5 - ECMA 3rd edition ▸ 2010: ECMA 5th edition ▸ 2015: ECMA 6th edition - ES6 / ES2015

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ENGINES ▸ JavaScriptCore ▸ V8 ▸ SpiderMonkey, Chakra, Carakan, …

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SWIFT & JAVASCRIPT SUPPORT DIFFERENT PROGRAMMING PARADIGMS.

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▸ Imperative Programming ▸ Object-oriented Programming ▸ Declarative Programming ▸ Functional Programming ▸ Many things in between …

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Let's talk about TYPES

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SWIFT HAS A STRONG TYPE SYSTEM.

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JAVASCRIPT HAS A DYNAMIC TYPE SYSTEM.

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INHERITANCE

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CLASSES IN SWIFT class Animal : CustomStringConvertible { var age: Int init(age: Int) { self.age = age } toString() { let className = String(describing: type(of: self)) return "\(className)(age: \(age))" } } class Dog : Animal { var furColor: String init(age: Int, furColor: String) { super(age: age) self.furColor = furColor; } }

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JAVASCRIPT HAS MANY ⠀ ⠀

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JAVASCRIPT'S PROTOTYPAL INHERITANCE function Animal(age) { this._age = age; } Object.defineProperty(Animal.prototype, "age", { get: function() { return this._age; }, }); Animal.prototype.toString = function() { return this.constructor.name + "(age: " + this.age + ")"; } function Dog(age, furColor) { Object.getPrototypeOf(Dog).call(this, age); this.furColor = furColor; } Dog.prototype = Object.create(Animal.prototype, { constructor: { value: Dog } });

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ES6 SYNTAX class Animal { constructor(age) { this._age = age; } get age() { return this._age; } toString() { return `${this.constructor.name}(age: ${this.age})`; } } class Dog extends Animal { constructor(age, furColor) { super(age); this.furColor = furColor; } }

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TYPESCRIPT class Animal { age: number; constructor(age: number) { this.age = age; } toString() { return `${this.constructor.name}(age: ${this.age})`; } } class Dog extends Animal { constructor(age: number, furColor: string) { super(age); this.furColor = furColor; } }

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WHY THE UGLY? UNDER THE HOOD IT'S STILL THE SAME!*

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EQUALITY?

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SWIFT HAS ==.

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SEMANTICS ARE ENCODED IN THE STANDARD LIBRARY AND EXTENSIBLE.

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extension Animal : Equatable {} public function ==(lhs: Animal, rhs: Animal) { return lhs.age == rhs.age; }

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JAVASCRIPT HAS MORE: == & ===

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===

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ROLL YOUR OWN class Animal { … isEqual(other) { return this.age === other.age; } }

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Let's talk about ⠀⠀⠀⠀⠀⠀⠀⠀⠀ null

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Swift has an explicit concept of nullability encoded in the type system.

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JavaScript hasn't. IN ADDITION TO null, EVERYTHING CAN BE undefined.

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null ▸ typeof null => "object" ▸ Literal

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undefined ▸ typeof undefined => "undefined" ▸ Property of the global object ▸ Can be overwritten !

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! TYPESCRIPT TO THE RESCUE!

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let u: undefined = undefined; let n: null = null;

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// In Swift func greet(name: string) { … } func greet(name: string?) { … }

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// In TypeScript // when compiled with --strictNullChecks function greet(name: string) { … } function greet(name: string | undefined = undefined) { … }

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ECO SYSTEM

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SWIFT RUNS ON … ▸ Mac and iOS devices ▸ Linux ▸ (Android) ▸ (Windows)

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JAVASCRIPT RUNS … everywhere

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JavaScript is an assembly language. — Erik Meijer

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ASM.JS

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Let's talk about ⠀⠀⠀⠀⠀⠀⠀⠀⠀ ⠀ ⠀ ⠀

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The Dream IMPLEMENT THE APP ONCE & DEPLOY IT ON ALL PLATFORMS

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REALITY? Platforms have different requirements!

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SHARE THE BUSINESS LOGIC But not UI ⠀ ⠀

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! DEPENDENCY MANAGEMENT

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Reminder SWIFT IS INTEROPERABLE WITH OBJECTIVE-C

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OBJECTIVE-C DEVELOPERS HISTORICALLY USED … ▸ No dependencies ▸ Git Submodules ▸ CocoaPods

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WITH SWIFT, MOST USE: ▸ CocoaPods ▸ Carthage ▸ Swift Package Manager

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NO CENTRAL CODE REGISTRY, YOU RELY ON PRIVATE HOSTED REPOSITORIES.

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JAVASCRIPT HAS … ▸ NPM for Node.js ▸ Different approaches for frontend code: Bower or Browserify / Webpack etc.

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NPM IS A PACKAGE MANAGER AND A PLATFORM.

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YOU SUBMIT ACTUAL CODE.

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! NO FULL DEPENDENCY RESOLUTION BY DEFAULT

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PITFALLS OF RECURSIVE RESOLUTION [email protected] !"" [email protected] # $"" [email protected] $"" [email protected]

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import BananaKit from 'bananakit'; import Monkey from 'monkey'; const monkey = new Monkey(); const tree = new BananaKit.Tree(); monkey.visit(tree); // => TypeError: m.climb is not a function // at tree.accept (bananakit.js) // at monkey.visit (monkey.js)

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DIFFERENT APPROACHES FOR LOCKING YOUR DEPENDENCIES ! ▸ Commit node_modules ▸ npm shrinkwrap ▸ Yarn