Geschrieben von Hussain Arif✏️
Stellen Sie sich eine Situation vor, in der eine Gruppe von Architekten einen Wolkenkratzer entwerfen möchte. Während der Entwurfsphase müssten sie eine Vielzahl von Faktoren berücksichtigen, zum Beispiel:
Es können viele Faktoren berücksichtigt werden, aber eines kann man mit Sicherheit wissen: Höchstwahrscheinlich liegt bereits ein Bauplan vor, der beim Bau dieses Wolkenkratzers helfen soll. Ohne einen gemeinsamen Entwurf oder Plan müssten diese Architekten das Rad neu erfinden, was zu Verwirrung und mehreren Ineffizienzen führen kann.
Ähnlich greifen Entwickler in der Programmierwelt häufig auf eine Reihe von Entwurfsmustern zurück, die ihnen beim Erstellen von Software helfen und dabei den Prinzipien des sauberen Codes folgen. Darüber hinaus sind diese Muster allgegenwärtig, sodass sich Programmierer auf die Bereitstellung neuer Funktionen konzentrieren können, anstatt das Rad jedes Mal neu erfinden zu müssen.
In diesem Artikel erfahren Sie mehr über einige häufig verwendete JavaScript-Entwurfsmuster. Gemeinsam erstellen wir kleine Node.js-Projekte, um die Verwendung jedes Entwurfsmusters zu veranschaulichen.
Designmuster sind vorgefertigte Blaupausen, die Entwickler anpassen können, um sich wiederholende Designprobleme während des Codierens zu lösen. Es ist wichtig zu bedenken, dass es sich bei diesen Blaupausen nicht um Codeschnipsel, sondern um allgemeine Konzepte zur Bewältigung kommender Herausforderungen handelt.
Designmuster haben viele Vorteile:
In diesem Artikel werden wir drei Kategorien von Designmustern behandeln:
Sehen wir uns diese Designmuster in Aktion an!
Wie der Name schon sagt, umfassen Erstellungsmuster verschiedene Methoden, die Entwicklern beim Erstellen von Objekten helfen.
Die Factory-Methode ist ein Muster zum Erstellen von Objekten, das mehr Kontrolle über die Objekterstellung ermöglicht. Diese Methode eignet sich für Fälle, in denen wir die Logik für die Objekterstellung an einem Ort zentralisieren möchten.
Hier ist ein Beispielcode, der dieses Muster in Aktion zeigt:
//file name: factory-pattern.js
//use the factory JavaScript design pattern:
//Step 1: Create an interface for our object. In this case, we want to create a car
const createCar = ({ company, model, size }) => ({
//the properties of the car:
company,
model,
size,
//a function that prints out the car's properties:
showDescription() {
console.log(
"The all new ",
model,
" is built by ",
company,
" and has an engine capacity of ",
size,
" CC "
);
},
});
//Use the 'createCar' interface to create a car
const challenger = createCar({
company: "Dodge",
model: "Challenger",
size: 6162,
});
//print out this object's traits:
challenger.showDescription();
Lassen Sie uns diesen Code Stück für Stück aufschlüsseln:createCarCar
Lass es uns testen! Wir sollten damit rechnen, dass das Programm die Details unserer neu erstellten Car-Instanz abmeldet: 
Mit der Builder-Methode können wir Objekte mithilfe der schrittweisen Objektkonstruktion erstellen. Daher eignet sich dieses Entwurfsmuster hervorragend für Situationen, in denen wir ein Objekt erstellen und nur die erforderlichen Funktionen anwenden möchten. Dies ermöglicht eine größere Flexibilität.
Hier ist ein Codeblock, der das Builder-Muster verwendet, um ein Car-Objekt zu erstellen:
//builder-pattern.js
//Step 1: Create a class reperesentation for our toy car:
class Car {
constructor({ model, company, size }) {
this.model = model;
this.company = company;
this.size = size;
}
}
//Use the 'builder' pattern to extend this class and add functions
//note that we have seperated these functions in their entities.
//this means that we have not defined these functions in the 'Car' definition.
Car.prototype.showDescription = function () {
console.log(
this.model +
" is made by " +
this.company +
" and has an engine capacity of " +
this.size +
" CC "
);
};
Car.prototype.reduceSize = function () {
const size = this.size - 2; //function to reduce the engine size of the car.
this.size = size;
};
const challenger = new Car({
company: "Dodge",
model: "Challenger",
size: 6162,
});
//finally, print out the properties of the car before and after reducing the size:
challenger.showDescription();
console.log('reducing size...');
//reduce size of car twice:
challenger.reduceSize();
challenger.reduceSize();
challenger.showDescription();
Das machen wir im obigen Codeblock:
The expected output should be the properties of the challenger object before and after we reduced its size by four units: 
This confirms that our builder pattern implementation in JavaScript was successful!
Structural design patterns focus on how different components of our program work together.
The adapter method allows objects with conflicting interfaces to work together. A great use case for this pattern is when we want to adapt old code to a new codebase without introducing breaking changes:
//adapter-pattern.js
//create an array with two fields:
//'name' of a band and the number of 'sold' albums
const groupsWithSoldAlbums = [
{
name: "Twice",
sold: 23,
},
{ name: "Blackpink", sold: 23 },
{ name: "Aespa", sold: 40 },
{ name: "NewJeans", sold: 45 },
];
console.log("Before:");
console.log(groupsWithSoldAlbums);
//now we want to add this object to the 'groupsWithSoldAlbums'
//problem: Our array can't accept the 'revenue' field
// we want to change this field to 'sold'
var illit = { name: "Illit", revenue: 300 };
//Solution: Create an 'adapter' to make both of these interfaces..
//..work with each other
const COST_PER_ALBUM = 30;
const convertToAlbumsSold = (group) => {
//make a copy of the object and change its properties
const tempGroup = { name: group.name, sold: 0 };
tempGroup.sold = parseInt(group.revenue / COST_PER_ALBUM);
//return this copy:
return tempGroup;
};
//use our adapter to make a compatible copy of the 'illit' object:
illit = convertToAlbumsSold(illit);
//now that our interfaces are compatible, we can add this object to the array
groupsWithSoldAlbums.push(illit);
console.log("After:");
console.log(groupsWithSoldAlbums);
Here’s what’s happening in this snippet:
When this code is run, we expect our illit object to be part of the groupsWithSoldAlbums list: 
This design pattern lets you add new methods and properties to objects after creation. This is useful when we want to extend the capabilities of a component during runtime.
If you come from a React background, this is similar to using Higher Order Components. Here is a block of code that demonstrates the use of the JavaScript decorator design pattern:
//file name: decorator-pattern.js
//Step 1: Create an interface
class MusicArtist {
constructor({ name, members }) {
this.name = name;
this.members = members;
}
displayMembers() {
console.log(
"Group name",
this.name,
" has",
this.members.length,
" members:"
);
this.members.map((item) => console.log(item));
}
}
//Step 2: Create another interface that extends the functionality of MusicArtist
class PerformingArtist extends MusicArtist {
constructor({ name, members, eventName, songName }) {
super({ name, members });
this.eventName = eventName;
this.songName = songName;
}
perform() {
console.log(
this.name +
" is now performing at " +
this.eventName +
" They will play their hit song " +
this.songName
);
}
}
//create an instance of PerformingArtist and print out its properties:
const akmu = new PerformingArtist({
name: "Akmu",
members: ["Suhyun", "Chanhyuk"],
eventName: "MNET",
songName: "Hero",
});
akmu.displayMembers();
akmu.perform();
Let's explain what's happening here:
The output of the code should confirm that we successfully added new capabilities to our music band via the PerformingArtist class: 
This category focuses on how different components in a program communicate with each other.
The Chain of Responsibility design pattern allows for passing requests through a chain of components. When the program receives a request, components in the chain either handle it or pass it on until the program finds a suitable handler.
Here’s an illustration that explains this design pattern: 
The bucket, or request, is passed down the chain of components until a capable component is found. When a suitable component is found, it will process the request. Source: Refactoring Guru.[/caption] The best use for this pattern is a chain of Express middleware functions, where a function would either process an incoming request or pass it to the next function via the next() method:
//Real-world situation: Event management of a concert
//implement COR JavaScript design pattern:
//Step 1: Create a class that will process a request
class Leader {
constructor(responsibility, name) {
this.responsibility = responsibility;
this.name = name;
}
//the 'setNext' function will pass the request to the next component in the chain.
setNext(handler) {
this.nextHandler = handler;
return handler;
}
handle(responsibility) {
//switch to the next handler and throw an error message:
if (this.nextHandler) {
console.log(this.name + " cannot handle operation: " + responsibility);
return this.nextHandler.handle(responsibility);
}
return false;
}
}
//create two components to handle certain requests of a concert
//first component: Handle the lighting of the concert:
class LightsEngineerLead extends Leader {
constructor(name) {
super("Light management", name);
}
handle(responsibility) {
//if 'LightsEngineerLead' gets the responsibility(request) to handle lights,
//then they will handle it
if (responsibility == "Lights") {
console.log("The lights are now being handled by ", this.name);
return;
}
//otherwise, pass it to the next component.
return super.handle(responsibility);
}
}
//second component: Handle the sound management of the event:
class SoundEngineerLead extends Leader {
constructor(name) {
super("Sound management", name);
}
handle(responsibility) {
//if 'SoundEngineerLead' gets the responsibility to handle sounds,
// they will handle it
if (responsibility == "Sound") {
console.log("The sound stage is now being handled by ", this.name);
return;
}
//otherwise, forward this request down the chain:
return super.handle(responsibility);
}
}
//create two instances to handle the lighting and sounds of an event:
const minji = new LightsEngineerLead("Minji");
const danielle = new SoundEngineerLead("Danielle");
//set 'danielle' to be the next handler component in the chain.
minji.setNext(danielle);
//ask Minji to handle the Sound and Lights:
//since Minji can't handle Sound Management,
// we expect this request to be forwarded
minji.handle("Sound");
//Minji can handle Lights, so we expect it to be processed
minji.handle("Lights");
In the above code, we’ve modeled a situation at a music concert. Here, we want different people to handle different responsibilities. If a person cannot handle a certain task, it’s delegated to the next person in the list.
Initially, we declared a Leader base class with two properties:
Additionally, each Leader will have two functions:
Next, we created two child classes called LightsEngineerLead (responsible for lighting), and SoundEngineerLead (handles audio). Later on, we initialized two objects — minji and danielle. We used the setNext function to set danielle as the next handler in the responsibility chain.
Lastly, we asked minji to handle Sound and Lights.
When the code is run, we expect minji to attempt at processing our Sound and Light responsibilities. Since minji is not an audio engineer, it should hand over Sound to a capable handler. In this case, it is danielle: 
The strategy method lets you define a collection of algorithms and swap between them during runtime. This pattern is useful for navigation apps. These apps can leverage this pattern to switch between routes for different user types (cycling, driving, or running):
This code block demonstrates the strategy design pattern in JavaScript code:
//situation: Build a calculator app that executes an operation between 2 numbers.
//depending on the user input, change between division and modulus operations
class CalculationStrategy {
performExecution(a, b) {}
}
//create an algorithm for division
class DivisionStrategy extends CalculationStrategy {
performExecution(a, b) {
return a / b;
}
}
//create another algorithm for performing modulus
class ModuloStrategy extends CalculationStrategy {
performExecution(a, b) {
return a % b;
}
}
//this class will help the program switch between our algorithms:
class StrategyManager {
setStrategy(strategy) {
this.strategy = strategy;
}
executeStrategy(a, b) {
return this.strategy.performExecution(a, b);
}
}
const moduloOperation = new ModuloStrategy();
const divisionOp = new DivisionStrategy();
const strategyManager = new StrategyManager();
//use the division algorithm to divide two numbers:
strategyManager.setStrategy(divisionOp);
var result = strategyManager.executeStrategy(20, 4);
console.log("Result is: ", result);
//switch to the modulus strategy to perform modulus:
strategyManager.setStrategy(moduloOperation);
result = strategyManager.executeStrategy(20, 4);
console.log("Result of modulo is ", result);
Here’s what we did in the above block:
When we execute this program, the expected output is strategyManager first using DivisionStrategy to divide two numbers and then switching to ModuloStrategy to return the modulo of those inputs: 
In this article, we learned about what design patterns are, and why they are useful in the software development industry. Furthermore, we also learned about different categories of JavaScript design patterns and implemented them in code.
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