Design Patterns

Women Techmakers Berlin

JavaScript Crash Course

Advanced lectures pt. 1

Armagan Amcalar

March 15th, 2018

Who am I?

Armagan Amcalar
Head of Software Engineering @ unu GmbH
Founder @ Lonca Works

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erste

cote

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brain-bits

pedalboard.js

tartJS
geneJS
jira-bot

AUTHORED ON GITHUB

Don’t forget…

This is a human story.

 

We write code for humans to understand.

 

That’s why it’s so complicated — it has direct interaction with human psychology.

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Background

Software development has a very high cognitive load
The job of a software developer is to solve complexity
The software we write grows daily
We hate the code we wrote 6 months ago
But we have to live with it for years to come

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Background

Code complexity should remain constant even if the code grows
Identification at first sight
What’s the secret?
    Only if they knew…

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Patterns everywhere

It’s about familiarity
Like signature stamps
   

 

 

 


Like paper money / bills  
Do you think machines are intelligent and they can learn?

Do you think they are better than humans at this?
    * They are taught to identify patterns

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pattern ˈpat(ə)n noun

 

  1. a repeated decorative design.
    synonyms:   design, decoration, motif, marking, ornament, ornamentation, device, figure
    "the pattern on the wallpaper"
     
  2. a regular and intelligible form or sequence discernible in the way in which something happens or is done.
    synonyms:   system, order, arrangement, method, sequence, structure, scheme, plan, form, format, framework, composition, constitution, shape, make-up, configuration
    "the ants' behaviour pattern"

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Some software principles

KISS

Keep it simple, stupid

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DRY

Do not repeat yourself

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SOLID

  • Single responsibility
  • Open/closed principle
  • Liskov substitution principle
  • Interface segregation
  • Dependency inversion

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More stuff you need to get familiar with

 

UML
Class diagrams
Sequence diagrams

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Design patterns

Categories

Creational
Structural
Behavioral

Creational patterns

Singleton

class Person {
    constructor() {
        if (typeof Person.instance === 'object') {
            return Person.instance;
        }
        Person.instance = this;
        return this;
    }
}

export default Person;

const john = new Person();
const john2 = new Person();
john === john2; // true

Factory

class BmwFactory {
    create(type) {
        if (type === 'X5')
            return new Bmw(type, 108000, 300);
        if (type === 'X6')
            return new Bmw(type, 111000, 320);
    }
}

class Bmw {
    constructor(model, price, maxSpeed) {
        this.model = model;
        this.price = price;
        this.maxSpeed = maxSpeed;
    }
}

export default BmwFactory;
const bmwFactory = new BmwFactory();
const x5 = bmwFactory.create('X5');
const x6 = bmwFactory.create('X6');

Structural patterns

Composite

//Equipment
class Equipment {
    getPrice() {
        return this.price || 0;
    }

    getName() {
        return this.name;
    }

    setName(name) {
        this.name = name;
    }
}

// --- composite ---
class Composite extends Equipment {
    constructor() {
        super();
        this.equipments = [];
    }

    add(equipment) {
        this.equipments.push(equipment);
    }

    getPrice() {
        return this.equipments.map(equipment => {
            return equipment.getPrice();
        }).reduce((a, b)  => {
            return  a + b;
        });
    }
}
class Cabinet extends Composite {
    constructor() {
        super();
        this.setName('cabinet');
    }
}

// --- leafs ---
class FloppyDisk extends Equipment {
    constructor() {
        super();
        this.setName('Floppy Disk');
        this.price = 70;
    }
}

class HardDrive extends Equipment {
    constructor() {
        super();
        this.setName('Hard Drive');
        this.price = 250;
    }
}

class Memory extends Equipment {
    constructor() {
        super();
        this.setName('Memory');
        this.price = 280;
    }
}
const cabinet = new Cabinet();
cabinet.add(new FloppyDisk());
cabinet.add(new HardDrive());
cabinet.add(new Memory());

cabinet.price; // 600

Decorator

class Pasta {
    constructor() {
        this.price = 0;
    }
    getPrice() {
        return this.price;
    }
}

class Penne extends Pasta {
    constructor() {
        super();
        this.price = 8;
    }
}

class PastaDecorator extends Pasta {
    constructor(pasta) {
        super();
        this.pasta = pasta;
    }

    getPrice() {
        return this.pasta.getPrice();
    }
}

class SauceDecorator extends PastaDecorator {
    constructor(pasta) {
        super(pasta);
    }

    getPrice() {
        return super.getPrice() + 5;
    }
}

class CheeseDecorator extends PastaDecorator {
    constructor(pasta) {
        super(pasta);
    }

    getPrice() {
        return super.getPrice() + 3;
    }
}

const penne = new Penne();
const penneWithSauce = new SauceDecorator(penne);
const penneWithSauceAndCheese = new CheeseDecorator(penneWithSauce);

penne.getPrice(); // 8
penneWithSauce.getPrice(); // 13
penneWithSauceAndCheese.getPrice(); // 16

Behavioral patterns

Strategy

class ShoppingCart {
    constructor(discount) {
        this.discount = discount;
        this.amount = 0;
    }

    checkout() {
        return this.discount(this.amount);
    }

    setAmount(amount) {
        this.amount = amount;
    }
}

function guestStrategy(amount) {
    return amount;
}

function regularStrategy(amount) {
    return amount * 0.9;
}

function premiumStrategy(amount) {
    return amount * 0.8;
}

export { ShoppingCart, guestStrategy, regularStrategy, premiumStrategy };

const guestCart = new ShoppingCart(guestStrategy);
guestCart.setAmount(100); 
guestCart.checkout(); // 100

const regularCart = new ShoppingCart(regularStrategy);
regularCart.setAmount(100);
regularCart.checkout(); // 90

const premiumCart = new ShoppingCart(premiumStrategy);
premiumCart.setAmount(100);
premiumCart.checkout(); // 80

Observer

Must reads

  • Design Patterns: Elements of Reusable Object-Oriented Software
  • Patterns of Enterprise Application Architecture
  • Clean Code
  • Clean Architecture
  • Pro JavaScript Design Patterns
  • Code Complete

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thank you!

Let's keep in touch!

Armagan Amcalar

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slides: https://slides.com/armaganamcalar/wtm-design-patterns

examples from https://github.com/fbeline/Design-Patterns-JS

Design Patterns

By Armağan Amcalar

Design Patterns

An introduction to popular software design patterns and how they can be utilized with JavaScript. In this session, we talk about what a design pattern is, what anti-patterns are, how they emerge and when to make use of one. We talk about some of the Gang of Four patterns and their applications.

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