endbander Interview Questions and Answers

1. What is the difference between == and === in JavaScript?

   • Answer: == performs loose equality comparison, checking for equality after type coercion. === performs strict equality comparison, checking for equality without type coercion. For example, 1 == "1" is true, but 1 === "1" is false.

2. Explain the concept of hoisting in JavaScript.

   • Answer: Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their scope before code execution. However, only declarations are hoisted, not initializations. This means a variable declared with var will be hoisted but will have a value of undefined before its actual declaration line.

3. What are closures in JavaScript?

   • Answer: A closure is a function that has access to the variables in its surrounding scope, even after that scope has finished executing. This allows inner functions to "remember" and access variables from their parent functions.

4. What is the difference between `let`, `const`, and `var` in JavaScript?

   • Answer: `var` has function scope or global scope, `let` and `const` have block scope. `const` declares a constant value, meaning it cannot be reassigned after initialization. `let` allows reassignment. `var` is generally discouraged in modern JavaScript in favor of `let` and `const` for better code clarity and preventing accidental reassignments.

5. Explain event delegation.

   • Answer: Event delegation is a technique where you attach an event listener to a parent element instead of individual child elements. When an event occurs on a child element, the event bubbles up to the parent, triggering the listener. This improves performance, especially with dynamically added elements.

6. What are promises in JavaScript?

   • Answer: Promises are objects that represent the eventual completion (or failure) of an asynchronous operation and its resulting value. They provide a cleaner way to handle asynchronous code than callbacks, using `.then()` for success and `.catch()` for error handling.

7. Explain async/await.

   • Answer: `async/await` is syntactic sugar built on top of promises, making asynchronous code look and behave a bit more like synchronous code. `async` makes a function return a promise, and `await` pauses execution until a promise resolves.

8. What is AJAX?

   • Answer: AJAX (Asynchronous JavaScript and XML) is a set of web development techniques using many web technologies on the client-side to asynchronously update parts of a web page without reloading the whole page.

9. What is the DOM?

   • Answer: The DOM (Document Object Model) is a programming interface for HTML and XML documents. It represents the page so that programs can change the document structure, style, and content.

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