Real interview questions from Pharmeasy company. Includes theoretical concepts and coding problems.
What are the key principles of object-oriented programming in JavaScript?
The key principles of object-oriented programming in JavaScript are encapsulation, inheritance, and polymorphism. Encapsulation refers to the idea of bundling data and methods that operate on that data within a single unit, called a class or object. Inheritance allows one class to inherit the properties and methods of another class, promoting code reuse and a hierarchical organization of code. Polymorphism is the ability of an object to take on multiple forms, depending on the context in which it is used, which can be achieved through method overriding or method overloading.
How does React handle state changes and component updates?
React handles state changes and component updates through a mechanism called the Virtual DOM. When the state of a component changes, React creates a new Virtual DOM tree and compares it with the previous Virtual DOM tree to determine the minimum number of changes needed to update the actual DOM. This process is called reconciliation. React then updates the actual DOM by applying these changes, which ensures efficient and optimized rendering of components.
What is the purpose of the 'this' keyword in JavaScript, and how does its value change based on the context of its use?
The 'this' keyword in JavaScript refers to the current execution context of a function. Its value can change based on how the function is called. In a global context, 'this' refers to the global object (usually the window object in a browser or the global object in a Node.js environment). When used within an object, 'this' refers to that object. The value of 'this' can also be explicitly set using methods like call(), apply(), or bind(), allowing for more control over the context in which a function is executed.
Explain the concept of a closure in JavaScript and provide an example of its use.
A closure in JavaScript is a function that has access to its outer function's scope, even when the outer function has returned. This allows the inner function to use variables from the outer function's scope, even after the outer function is no longer executing. An example of a closure is when a function returns another function, and the returned function uses variables from the outer function's scope. Closures are useful for creating private variables and functions, and for encapsulating data and behavior.
What are the differences between null and undefined in JavaScript?
In JavaScript, null and undefined are two distinct primitive values that are often confused with each other due to their similar roles in representing the absence of a value. Null represents the intentional absence of any object value, which is a primitive value that represents the null, or non-existent, object reference. Undefined, on the other hand, represents an uninitialized variable or a non-existent property of an object. While both can be used to check for missing values, they have different use cases and implications in JavaScript programming.
How does JavaScript's asynchronous nature affect the way you write code, especially in terms of handling callbacks and promises?
JavaScript's asynchronous nature significantly affects how code is written, particularly in handling callbacks and promises. Asynchronous operations, such as network requests or database queries, do not block the execution of the code. Instead, they use callbacks or return promises that are resolved when the operation is complete. This requires developers to structure their code to handle these asynchronous operations, often using techniques like callback chaining, promise chaining, or async/await syntax to manage complexity and ensure that code executes in the expected order.
What are the benefits and drawbacks of using a framework like React for front-end development?
The benefits of using a framework like React for front-end development include its component-based architecture, which promotes code reuse and modularity, and its efficient handling of state changes and component updates through the Virtual DOM. Additionally, React has a large and active community, which means there are many resources available for learning and troubleshooting. However, drawbacks include the initial learning curve, especially for developers without prior experience in component-based frameworks, and the potential for over-engineering simple applications. Furthermore, React requires additional libraries for state management and routing, which can add complexity to the project.
Explain the concept of a singleton pattern in JavaScript and how it can be implemented.
The singleton pattern is a design pattern that restricts a class from instantiating multiple objects. It creates a single instance of a class and provides a global point of access to that instance. In JavaScript, the singleton pattern can be implemented using a function that returns an object. If the object has already been created, the function returns the existing object; otherwise, it creates a new object and returns it. This ensures that only one instance of the object is ever created, and it provides a global point of access to that instance.
What are the key differences between JavaScript's var, let, and const keywords for variable declaration?
The key differences between JavaScript's var, let, and const keywords for variable declaration are their scope, hoisting behavior, and the ability to reassign values. Var has a function scope and is hoisted to the top of its scope, regardless of where the actual declaration is made. Let and const have a block scope and are not hoisted in the same way as var; they are part of a concept called the Temporal Dead Zone, where they cannot be accessed until they are declared. Additionally, var allows reassignment and redeclaration, let allows reassignment but not redeclaration, and const does not allow either reassignment or redeclaration.
How does Node.js handle concurrency, and what are the implications for writing scalable server-side applications?
Node.js handles concurrency through its event-driven, non-blocking I/O model. This means that instead of blocking on I/O operations like network requests or file access, Node.js uses callbacks or promises to handle the response when the operation is complete. This allows Node.js to handle a large number of concurrent connections without the need for multiple threads, making it highly scalable for server-side applications. However, it also requires developers to write asynchronous code that can manage these concurrent operations efficiently, often using techniques like async/await or promise chaining.
Explain the concept of dependency injection in JavaScript and its benefits for modular and testable code.
Dependency injection is a design pattern that allows components to be loosely coupled, making it easier to test, maintain, and extend the system. In JavaScript, dependency injection involves passing dependencies into a component rather than the component creating its own dependencies. This decouples the component from specific implementations of its dependencies, allowing for greater flexibility and testability. The benefits include making the code more modular, easier to test, and less prone to tight coupling, which can lead to rigid and fragile systems.
What are the advantages and disadvantages of using a state management library like Redux in a React application?
The advantages of using a state management library like Redux in a React application include its ability to manage global state by providing a single source of truth for state, making it easier to debug and understand how state changes affect the application. Redux also promotes predictable behavior and makes it easier to implement features like undo/redo. However, the disadvantages include the added complexity of setting up and managing the Redux store, the potential for over-engineering simple applications, and the learning curve for developers without prior experience with state management libraries.
How does JavaScript's prototype chain work, and what are its implications for object inheritance?
JavaScript's prototype chain is a mechanism by which objects inherit properties from one another. When a property is accessed on an object, JavaScript first checks if the object has its own property with that name. If not, it checks the object's prototype, and then the prototype's prototype, and so on, until it reaches the end of the prototype chain. This allows for a flexible and dynamic form of inheritance, where objects can inherit behavior from other objects without the need for a rigid class hierarchy.
Explain the concept of memoization in JavaScript and how it can be used to optimize function performance.
Memoization is an optimization technique that stores the results of expensive function calls so that they can be reused instead of recalculated. In JavaScript, memoization can be implemented using a cache object that stores the results of function calls based on their input parameters. Before computing a result, the function checks the cache to see if the result for the given input parameters already exists. If it does, the cached result is returned; otherwise, the result is computed, stored in the cache, and then returned. This technique is particularly useful for optimizing functions that perform complex computations or make expensive network requests.
Write a JavaScript function that takes a string as input and returns the string with all vowels removed.
