JavaScript has become an essential language for web development, and with the ever-growing complexity of web applications, it’s crucial for developers to adopt best practices for code organization.
JavaScript design patterns play a pivotal role in structuring code and making it more maintainable, scalable, and efficient.
In this comprehensive guide, we’ll explore popular design patterns, their implementation, and the benefits they bring to your projects.
Module Pattern
The Module Pattern is widely used in JavaScript development as a means to encapsulate and organize code.
It provides a way to create private and public methods, variables, and namespaces, preventing global scope pollution and promoting modularity.
Example:
const myModule = (function() {
let privateVar = "I am a private variable";
function privateMethod() {
console.log("I am a private method");
}
return {
publicVar: "I am a public variable",
publicMethod: function() {
console.log("I am a public method");
privateMethod();
},
};
})();
console.log(myModule.publicVar); // "I am a public variable"
myModule.publicMethod(); // "I am a public method" & "I am a private method"
Revealing Module Pattern
The Revealing Module Pattern is a variation of the Module Pattern that exposes only specific parts of the module, making it easier to manage and understand the exposed API.
Example:
const myRevealingModule = (function() {
let privateVar = "I am a private variable";
function privateMethod() {
console.log("I am a private method");
}
function publicMethod() {
console.log("I am a public method");
privateMethod();
}
return {
publicVar: "I am a public variable",
publicMethod,
};
})();
console.log(myRevealingModule.publicVar); // "I am a public variable"
myRevealingModule.publicMethod(); // "I am a public method" & "I am a private method"
Singleton Pattern
The Singleton Pattern ensures that a class has only one instance, providing a global point of access to it. This pattern is useful when you need to coordinate actions across a system and share resources efficiently.
Example:
class Singleton {
constructor(data) {
if (Singleton.instance) {
return Singleton.instance;
}
Singleton.instance = this;
this.data = data;
}
getData() {
return this.data;
}
}
const instanceA = new Singleton("Data for instance A");
const instanceB = new Singleton("Data for instance B");
console.log(instanceA.getData()); // "Data for instance A"
console.log(instanceB.getData()); // "Data for instance A"
Factory Pattern
The Factory Pattern is a creational pattern that provides an interface for creating objects in a superclass, allowing subclasses to alter the type of objects that will be created. It promotes loose coupling by eliminating the need to bind application-specific classes into the code.
Example:
class ShapeFactory {
createShape(type) {
switch (type) {
case "circle":
return new Circle();
case "rectangle":
return new Rectangle();
default:
throw new Error("Invalid shape type");
}
}
}
class Circle {
draw() {
console.log("Drawing a circle");
}
}
class Rectangle {
draw() {
console.log("Drawing a rectangle");
}
}
const factory = new ShapeFactory();
const circle = factory.createShape("circle");
circle.draw(); // "Drawing a circle"
const rectangle = factory.createShape("rectangle");
rectangle.draw(); // "Drawing a rectangle"
Observer Pattern
The Observer Pattern is a behavioral design pattern that defines a one-to-many dependency between objects. When the state of one object (the subject) changes, all its dependents (observers) are notified and updated automatically.
Example:
class Subject {
constructor() {
this.observers = [];
}
addObserver(observer) {
this.observers.push(observer);
}
removeObserver(observer) {
this.observers = this.observers.filter((obs) => obs !== observer);
}
notify(data) {
this.observers.forEach((observer) => observer.update(data));
}
}
class Observer {
update(data) {
console.log("Observer updated with data:", data);
}
}
const subject = new Subject();
const observerA = new Observer();
const observerB = new Observer();
subject.addObserver(observerA);
subject.addObserver(observerB);
subject.notify("Hello, observers!"); // Observer updated with data: Hello, observers!
Mediator Pattern
The Mediator Pattern defines an object that encapsulates how a set of objects interact, promoting loose coupling by keeping objects from referring to each other explicitly. It can be useful for coordinating the behavior of multiple objects in a complex system.
Example:
class Mediator {
constructor() {
this.channels = {};
}
subscribe(channel, callback) {
if (!this.channels[channel]) {
this.channels[channel] = [];
}
this.channels[channel].push(callback);
}
publish(channel, data) {
if (this.channels[channel]) {
this.channels[channel].forEach((callback) => callback(data));
}
}
}
const mediator = new Mediator();
mediator.subscribe("notification", (data) => {
console.log("Subscriber 1 received:", data);
});
mediator.subscribe("notification", (data) => {
console.log("Subscriber 2 received:", data);
});
mediator.publish("notification", "Hello, subscribers!"); // Subscriber 1 received: Hello, subscribers!
// Subscriber 2 received: Hello, subscribers!
Prototype Pattern
The Prototype Pattern is a creational design pattern that uses an existing object as a prototype to create new objects with the same properties. It can be useful when the construction of a new object is expensive or complex.
Example:
class Car {
constructor(make, model, year) {
this.make = make;
this.model = model;
this.year = year;
}
clone() {
return new Car(this.make, this.model, this.year);
}
}
const originalCar = new Car("Toyota", "Camry", 2021);
const clonedCar = originalCar.clone();
console.log(clonedCar.make); // "Toyota"
console.log(clonedCar.model); // "Camry"
console.log(clonedCar.year); // 2021
Decorator Pattern
The Decorator Pattern is a structural design pattern that involves a set of decorator classes that are used to wrap concrete components. Decorator classes mirror the type of the components they decorate but add or override behavior.
Example:
class Coffee {
cost() {
return 2;
}
}
class MilkDecorator {
constructor(coffee) {
this.coffee = coffee;
}
cost() {
return this.coffee.cost() + 0.5;
}
}
class SugarDecorator {
constructor(coffee) {
this.coffee = coffee;
}
cost() {
return this.coffee.cost() + 0.3;
}
}
const plainCoffee = new Coffee();
const coffeeWithMilk = new MilkDecorator(plainCoffee);
const coffeeWithMilkAndSugar = new SugarDecorator(coffeeWithMilk);
console.log(plainCoffee.cost()); // 2
console.log(coffeeWithMilk.cost()); // 2.5
console.log(coffeeWithMilkAndSugar.cost()); // 2.8
Facade Pattern
The Facade Pattern provides a simplified interface to a more complex subsystem. It reduces the learning curve and dependencies on the subsystem by hiding its complexity behind a unified interface.
Example:
class ComplexSubSystem {
methodA() {
console.log("Performing complex operation A");
}
methodB() {
console.log("Performing complex operation B");
}
}
class Facade {
constructor() {
this.subSystem = new ComplexSubSystem();
}
simplifiedMethod() {
this.subSystem.methodA();
this.subSystem.methodB();
}
}
const facade = new Facade();
facade.simplifiedMethod();
// Performing complex operation A
// Performing complex operation BCommand Pattern
The Command Pattern is a behavioral design pattern that encapsulates a request as an object, allowing you to parameterize clients with different requests, queue or log requests, and support undoable operations.
Example:
class Command {
constructor(receiver, action, value) {
this.receiver = receiver;
this.action = action;
this.value = value;
}
execute() {
this.receiver[this.action](this.value);
}
}
class Calculator {
constructor() {
this.value = 0;
}
add(number) {
this.value += number;
}
subtract(number) {
this.value -= number;
}
}
const calculator = new Calculator();
const addCommand = new Command(calculator, "add", 10);
const subtractCommand = new Command(calculator, "subtract", 5);
addCommand.execute(); // calculator.value is now 10
subtractCommand.execute(); // calculator.value is now 5
Summary
In this comprehensive guide, we’ve explored popular JavaScript design patterns and their applications, along with relevant code samples and scenarios.
These patterns help you organize and structure your code, making it more maintainable, scalable, and efficient.
By understanding and applying these design patterns, you can improve the overall quality of your projects and become a more proficient JavaScript developer.
So, keep practicing and keep improving! 😊
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