1. Explain closures in JavaScript.
Closures are functions that have access to their outer function's scope, even after the outer function has finished executing.
2. What are higher-order functions in JavaScript?
Higher-order functions are functions that operate on other functions, either by taking them as arguments or by returning them.
3. What is a callback function?
A callback function is a function passed as an argument to another function, which is then invoked inside the outer function to complete some kind of routine or action.
4. What is event delegation in JavaScript?
Event delegation is a technique where a single event listener is attached to a parent element to listen for events that occur on its children. This is particularly useful when dealing with dynamically added elements.
5. Explain the concept of prototypal inheritance in JavaScript.
Prototypal inheritance is the mechanism by which objects in JavaScript inherit properties and methods from other objects, known as prototypes.
6. What is the this keyword in JavaScript?
The this keyword refers to the object on which a method is being invoked or the context in which a function is called.
7. How does JavaScript handle asynchronous operations?
JavaScript uses mechanisms such as callbacks, promises, and async/await to handle asynchronous operations.
8. What are JavaScript promises?
Promises are objects representing the eventual completion or failure of an asynchronous operation, and they allow for more readable and manageable asynchronous code.
9. Explain the difference between null and undefined in JavaScript.
null represents the intentional absence of any object value, while undefined represents the absence of a defined value.
10. What is the event loop in JavaScript?
The event loop is a mechanism that handles asynchronous operations in JavaScript, ensuring that they are executed in a non-blocking manner.
11. What is the difference between null, undefined, and undeclared in JavaScript?
null is an explicitly assigned value that represents the absence of any object value, undefined indicates a variable that has been declared but has not yet been assigned a value, and undeclared refers to variables that have not been declared at all.
12. Explain the concept of event-driven programming in JavaScript.
Event-driven programming is a paradigm where the flow of the program is determined by events such as user actions, network requests, or timer events, rather than being strictly sequential.
13. What is the difference between synchronous and asynchronous JavaScript?
Synchronous JavaScript executes code sequentially, blocking further execution until the current operation is completed, whereas asynchronous JavaScript allows multiple operations to be executed concurrently, without blocking the main execution thread.
14. How do you handle errors in JavaScript?
Errors in JavaScript can be handled using try-catch blocks to catch exceptions and handle them gracefully, preventing the program from crashing.
15. What are JavaScript modules and how do they improve code organization?
JavaScript modules are reusable pieces of code that encapsulate related functionality and are designed to promote modularity, encapsulation, and code reuse, leading to better code organization and maintainability