 |
VOOZH | about |
|
VOOZH | about |
The Design Patterns are basically defined as the reusable and generalized solutions to the common problems that arise during software design and development. Design patterns are not specific to any particular programming language or technology instead, they provide abstract templates or blueprints for solving recurring design-related problems. They help software developers create well-structured, maintainable, and flexible code by promoting best practices and proven solutions.
JavaScript Design Patterns Interview Questions
A design pattern is the reusable solution to the common problem in software design and software development. It is basically a general template that can be applied to solve a particular design problem in code.
There are mainly three types of design patterns:
There are so many advantages of using design pattern let's see some of them are:
The module pattern is used in JavaScript to provide a structure for organizing code into reusable and maintainable modules. It provides a way to encapsulate variables and functions within a single unit of code, making it easier to manage complex applications.
Let's understand by the help of example:
I am public This is a public function I am private This is a private function
The Observer pattern defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
Example:
Observer 1 has been notified of the state change. Observer 2 has been notified of the state change.
In this example, Subject maintains a list of observers, and when its state changes (using the setState method), it notifies all registered observers through the notifyObservers method. Observers, in turn, implement an update method to define what actions they should take when notified.
The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance. It is often used for logging, driver objects, caching, thread pools, or database connections.
true I am a singleton instance!
In this example, the Singleton module is an immediately invoked function expression (IIFE) that encapsulates the logic for creating a singleton instance. The instance variable is used to store the reference to the single instance.
Strategy pattern is a behavioral design pattern that allows the behavior of an object to be selected at runtime. It is one of the Gang of Four (GoF) design patterns, which are widely used in object-oriented programming.
The Strategy pattern is based on the idea of encapsulating a family of algorithms into separate classes that implement a common interface. The pattern consists of three main components: the Context, the Strategy, and the Concrete Strategy.
Here's a simple example to illustrate how it works:
Executing Strategy A Executing Strategy B
In this example, we have two strategies (strategyA and strategyB) that encapsulate different algorithms. The Context object is responsible for using the current strategy and can switch between different strategies at runtime using the setStrategy method.
The factory method is a creational design pattern, i.e., related to object creation. The Factory Method pattern is used to create objects without specifying the exact class of object that will be created. This pattern is useful when you need to decouple the creation of an object from its implementation.
Car { model: 'Toyota', year: 2022 }
Car { model: 'Honda', year: 2023 }The Prototype pattern creates new objects by copying an existing object, known as the prototype. It is useful when creating many similar objects.
Example:
Driving the car! Stopping the car!
The Decorator pattern allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class.
8
The four authors who published the book Design Patterns Elements of Reusable Object-Oriented Software are known as Gang of Four. The name of four authors are Erich Gamma, Ralph Johnson, Richard Hel, and John Vlissides.
MVC is an architectural design pattern that separates an application into three interconnected components: Model (data and business logic), View (user interface), and Controller (handles user input and updates the model and view).
One of the most commonly used design patterns in JavaScript is the Module Pattern. The Module Pattern is a way to encapsulate a set of functionalities, creating a modular and organized structure for your code. It leverages closures to provide private and public members, allowing for better control over the scope and access to variables and functions.
The Dependency Injection pattern involves supplying an external dependency to a software component rather than creating it within the component. In JavaScript, this can be achieved through constructor injection or property injection.
The Publish-Subscribe pattern, also known as the Observer pattern, allows multiple objects to listen and respond to events. This pattern is used to establish communication between objects without them being directly coupled.
Subscriber 1 received news: Breaking News: Important event! Subscriber 2 received news: Breaking News: Important event!
The Strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable and the State pattern allows an object to alter its behavior when its internal state changes.
The Proxy pattern provides a surrogate or placeholder for another object to control access to it. It is useful for implementing lazy loading, access control, and logging.
Let's see a simple example of using the Proxy pattern to create a basic logging proxy:
Real subject handles the request.
In this example, the proxy object intercepts the request operation and logs a message before forwarding the request to the realSubject. You can customize the behavior of the proxy by defining different traps in the handler object.
The Template Method pattern defines the skeleton of an algorithm in the superclass but lets subclasses override specific steps of the algorithm without changing its structure.
Example:
AbstractClass: Step 1 ConcreteClass: Step 2 overridden AbstractClass: Step 3
The Chain of Responsibility pattern passes a request along a chain of handlers. In JavaScript, this is often used in event handling where multiple objects can handle an event, and the event is passed through a chain of handlers until one handles it.
Manager approved the expense request of $800 Manager cannot approve. Passing to Director Director approved the expense request of $4500 Manager cannot approve. Passing to Director Director cannot appr...
The Factory pattern involves creating objects through a common interface, while the Abstract Factory pattern provides an interface for creating families of related or dependent objects without specifying their concrete classes.
The Proxy pattern provides a surrogate or placeholder for another object to control access to it. In JavaScript, a common example is the Proxy API, which allows you to create a proxy for another object with custom behavior.
ProxySubject: Performing pre-request actions RealSubject: Handling request ProxySubject: Performing post-request actions
The Command pattern involves encapsulating a request as an object, allowing for parameterization of clients with different requests, queuing of requests, and logging of the requests. In JavaScript, it's commonly used in UI components and event handling.
The Memento pattern captures and externalizes an object's internal state so that the object can be restored to this state later.
Let's see the example:
Current State: Initial State Current State: Modified State Current State: Initial State
The Revealing Module pattern is defined as an extension of the Module pattern, where only the parts of the module pattern that should be public are revealed, and keeping the rest private.
The State Pattern basically allows an object to alter its behavior when its internal state changes. The pattern represents states as separate classes and delegates the state-specific behavior to these classes. This can make the object's behavior more modular and easier to extend.
Handling state 1 Handling state 2
Flux is an architectural pattern used in building client-side web applications. It involves unidirectional data flow and uses the Observer Pattern to handle updates between different components of the application. It's commonly associated with React applications.
The Module Pattern is a way to encapsulate private and public members using closures. The Revealing Module Pattern is a variation where the pattern reveals only the necessary functions and properties.
The Flux Pattern is an architecture for managing state in a JavaScript application. It is commonly associated with React.js. The key components are the dispatcher, stores, and views. Actions trigger updates in the stores, which then notify the views to re-render. This unidirectional flow helps in managing complex state in large applications.
These interview questions of design pattern in JavaScript cover a wide range of topics related to design patterns in JavaScript and software design principles. Preparing answers to these questions will help you demonstrate your understanding of JavaScript design patterns and their practical applications in interviews.