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When hiring someone with a lot of experience, interviewers usually don’t ask candidates how well they know the syntax of a certain language. Instead, they ask questions that test the candidate’s skill and experience with software design patterns.
Software design questions demonstrate your critical thinking, problem-solving skills, and ability to optimize or scale a given problem. Learning how to effectively deploy design patterns empowers you to answer any coding challenge.
This article will explain what design patterns are and show you how to use a few of them by giving you real-life problems to solve.
Ace Your JavaScript Design Pattern Interviews with This Comprehensive Guide
If you want to stand out in the fast-paced world of web development, you need to learn JavaScript design patterns. You will be a great asset to any development team if you can use these solutions to common problems again and again. They will help you write code that is cleaner, easier to maintain, and more efficient. Whether you’re a seasoned developer or just starting out, learning and using design patterns will make your coding skills a lot better.
This detailed guide goes into detail about the top 30 JavaScript design patterns that are often asked about in job interviews. It gives you the knowledge and confidence to handle any challenge that comes your way.
What are Design Patterns?
Before diving into specific patterns, let’s establish a clear understanding of what they are. Design patterns are essentially blueprints for solving recurring problems in software development. They provide proven reusable solutions that can be applied across different projects and contexts. By leveraging these patterns, you can avoid reinventing the wheel and focus on building innovative and robust applications.
Benefits of Using Design Patterns in JavaScript
- Reusability: Design patterns are inherently reusable, saving you time and effort by providing pre-built solutions to common problems.
- Maintainability: Code written using design patterns is easier to understand, maintain, and modify, making it a breeze to collaborate with other developers.
- Scalability: Design patterns promote modularity and separation of concerns, making it easier to scale your application as it grows in complexity.
- Flexibility: Design patterns offer flexibility by providing multiple solutions to the same problem, allowing you to choose the most appropriate option for your specific needs.
- Communication: Design patterns act as a common language among developers, facilitating effective communication and collaboration within your team.
Top 30 JavaScript Design Pattern Interview Questions
Now, let’s delve into the heart of this guide: the top 30 JavaScript design patterns that you’re likely to encounter in interviews. Each pattern is explained in detail, with examples to illustrate its implementation and usage.
1 Singleton Pattern
The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance. It’s often used for logging, driver objects, caching, thread pools, or database connections.
2. Observer Pattern
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. This pattern is commonly used for event handling, data binding, and asynchronous operations.
3. Factory Pattern
The Factory pattern is a creational design pattern that allows you 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
4. Strategy Pattern
The Strategy pattern allows you to select the behavior of an object at runtime. This pattern is useful when you have multiple algorithms that can be used to solve a problem, and you want to choose the most appropriate algorithm at runtime.
5. Prototype Pattern
The Prototype pattern creates new objects by copying an existing object, known as the prototype. This pattern is useful when creating many similar objects.
6. Decorator Pattern
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. This pattern is useful for extending the functionality of objects without modifying their underlying structure.
7. 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.
8. Dependency Injection Pattern
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.
9. Publish-Subscribe Pattern
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.
10. MVC (Model-View-Controller) Pattern
The MVC pattern 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).
11. Gang of Four (GoF) Design Patterns
The Gang of Four (GoF) refers to the four authors who published the book “Design Patterns: Elements of Reusable Object-Oriented Software.” The book outlines 23 classic design patterns, many of which are applicable to JavaScript development.
12. Strategy vs. State Pattern
The Strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. The State pattern allows an object to alter its behavior when its internal state changes. While both patterns deal with changing behavior, they do so in different ways.
13. Proxy Pattern
The Proxy pattern provides a surrogate or placeholder for another object to control access to it. It’s useful for implementing lazy loading, access control, and logging.
14. Template Method Pattern
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. This pattern is useful for defining algorithms with common steps and variations.
15. Chain of Responsibility Pattern
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.
16. Command Pattern
The Command pattern encapsulates a request as an object, allowing for the parameterization of clients with different requests, queuing or logging of requests, and support for undoable operations.
17. Memento Pattern
The Memento pattern provides a way to restore an object to a previous state (checkpoint). This pattern is useful for implementing undo/redo functionality or for creating snapshots of an object’s state.
18. Iterator Pattern
The Iterator pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation. This pattern is useful for traversing collections of objects in a uniform way.
19. Adapter Pattern
The Adapter pattern allows objects with incompatible interfaces to work together by converting the interface of one object into an interface expected by the other. This pattern is useful for integrating legacy systems or third-party libraries into your application.
20. Facade Pattern
The Facade pattern provides a simplified interface to a complex system, hiding the underlying complexity from the user. This pattern is useful for making a system easier to use and understand.
21. Mediator Pattern
The Mediator pattern defines an object that encapsulates how a set of objects interact. This pattern is useful for reducing communication complexity between multiple objects or for promoting loose coupling between them.
22. Visitor Pattern
The Visitor pattern represents an operation to be performed on the elements of an object structure. This pattern is useful for adding new operations to an existing object structure without modifying the structure itself.
23. Composite Pattern
The Composite pattern composes objects into tree structures to represent part-whole hierarchies. This pattern is useful for modeling tree-structured data or for implementing recursive algorithms.
24. State Pattern
The State pattern allows an object to alter its behavior when its internal state changes. This pattern is useful for modeling objects that have different behaviors depending on their state.
25. Flyweight Pattern
The Flyweight pattern uses sharing to support large numbers of fine-grained objects efficiently. This pattern is useful for optimizing memory usage when dealing with a large number of similar objects.
26. Observer Pattern (Again!)
The Observer pattern is so important that it deserves a second mention. This pattern is a fundamental building block for many other design patterns and is essential for creating loosely coupled and event-driven systems.
27. Revealing Module Pattern
The Revealing Module pattern is a way to create modules that encapsulate their internal state and expose only a public API. This pattern is useful for organizing code into modules and for hiding implementation details from the outside world.
28. Factory Pattern vs. Abstract Factory Pattern
The Factory pattern creates objects without specifying the exact class of object that will be created. The Abstract Factory pattern creates families of related objects without specifying their concrete classes. Both patterns are useful for decoupling object creation from implementation, but the Abstract Factory pattern provides a way to create multiple related objects at once.
29. Flux Pattern
The Flux pattern is a unidirectional data flow architecture that is often used with React. It utilizes the Observer pattern to propagate changes through the application.
30. Module Pattern vs. Revealing Module Pattern
The Module pattern and the Revealing Module pattern are both ways to create modules that encapsulate their internal state and expose only a public API. The main difference is that the Module pattern returns an object that contains both public and private members, while the Revealing Module pattern returns only the public members.
Mastering JavaScript design patterns is an essential step in becoming a skilled and efficient developer. By understanding and applying these patterns, you can write cleaner, more maintainable, and scalable code, making you a valuable asset to any development team.
This guide has provided you with a comprehensive overview of the top 30 JavaScript design patterns that frequently appear in interviews. Use this knowledge to confidently tackle any design pattern challenge that comes your way and
Challenge #1: Factory Pattern
In this problem, we will be implementing another factory called ToyFactory. It should be able to use either the ToyDuck or ToyCar function constructor to make the duck and car toys. The ToyDuck should have the following properties: color & price. The ToyCar should have the following properties: color, price, and name. So, let’s first create a function: createToy. This should decide which toy to create depending on the parameter we pass to it. Try it yourself below and then click on the tab to see the solution. We will discuss the solution piece by piece.
Alright, so we wanted to create the function createToy that would make either a ToyCar or ToyDuck. In the solution, we started by defining these constructor functions:
- ToyDuck() accepts a parameter toyObj. The object sets its color equal to toyObj. color and its price equal to toyObj. price, as we define them to be.
- ToyCar() accepts a parameter toyObj. The object sets its color equal to toyObj. color, its price equal to toyObj. price, and its name equal to toyObj. name, as we define them to be.
Now that the constructor functions are set, we use the createToy method, which is set in the ToyFactory constructor function, to put the factory pattern into action. The createToy method accepts a parameter toyChosen. This parameter has a property, toyType, which stores the type of the toy. Depending on its value, it sets the value of toy equal to either ToyDuck class or ToyCar class. The function’s return value is an object instance of the required class. Let’s look at that in code:
The factory pattern is a creational pattern that is often used in system design questions. You should now understand how it works. As I already said, the Constructor Pattern, the Singleton Pattern, the Builder Pattern, the Prototype Pattern, and the Abstract Pattern are some other common patterns.
After that, we’ll look at Structural Patterns and use one of them to solve a coding problem.
What are Design Patterns?
In software engineering, a design pattern is a general, reusable way to solve a problem that comes up often, like making JavaScript web apps or designing a standard computer system.
A design pattern is not a ready-to-use solution; instead, it gives you a way to describe or organize how to solve a problem. You can use it in different situations. These patterns allow us to reuse code structure for specific system design problems. %0 node_1 Publisher node_2 Subscriber node_1->node_2 node_3 Subscriber node_1->node_3 node_4 Subscriber node_1->node_4 node_1594931190751 Subscriber node_1->node_1594931190751 node_1594931193126 Subscriber node_1->node_1594931193126.
The illustration above shows an example of a commonly used design pattern: the observer pattern. This is helpful in situations where one object (the publisher) can change other objects (the subscribers), but the subscribers don’t have any say over when or how these changes happen. Using a design pattern has many advantages:
- They offer standard templates that can fix a lot of common issues.
- Because other developers can build on a pattern, code structure doesn’t take as much time.
- Because design patterns offer better ways to do things, they make code bases smaller.
- They’re the best solution that experienced programmers have come up with, so you can trust the results and how well they work.
For a senior developer coding interview, design questions will be baked into the coding questions you face. There isn’t a separate interview for design, so you should be ready to be asked about system design at any point.
10 Design Patterns Explained in 10 Minutes
FAQ
What is the most common design pattern asked in an interview?
Can you use design patterns in JavaScript?
What is a JavaScript design pattern interview question?
Design patterns provide proven solutions to common problems that developers encounter in software development. In JavaScript design pattern interview questions, candidates can expect questions that test their understanding of how to apply these patterns in a practical context.
How do I prepare for a JavaScript interview?
Consistent practice is the key! To get you started, I recommend Educative’s course JavaScript Design Patterns for Coding Interviews, which will adequately prepare you for all the aspects of an interview process. This course is designed around the main design patterns.
How many JavaScript interview questions are there?
These questions can range from basic to highly complex, and require a strong understanding of JavaScript fundamentals, as well as familiarity with common design patterns and their implementation. In this article, we’ll provide 60 interview questions and answers that cover a wide range of JavaScript design patterns.
Should you use a design pattern for a coding interview?
Using a design pattern has many advantages: For a senior developer coding interview, design questions will be baked into the coding questions you face. There is no separate design interview, so you should be prepared to face system design questions at any stage.
