end maker Interview Questions and Answers

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100 Frontend Maker Interview Questions and Answers

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

    • Answer: `==` performs loose equality comparison, coercing the operands to the same type before comparison. `===` performs strict equality comparison, checking for both value and type 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 declarations of variables and functions are moved to the top of their scope before code execution. This means you can use a variable or function before its declaration, but only if it's declared with `var` (function declarations are always hoisted). However, the value will be `undefined` for variables until the line of the actual declaration is reached. Using `let` and `const` prevents hoisting in the same way, resulting in a `ReferenceError` if you try to use them before their declaration.

  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 use variables from their parent function's scope, even after the parent function has returned.

  4. Explain the difference between `let`, `const`, and `var` in JavaScript.

    • Answer: `var` has function scope or global scope. `let` and `const` have block scope (within `{}`). `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 readability and preventing accidental reassignments.

  5. What is the event loop in JavaScript?

    • Answer: The JavaScript event loop is a mechanism that allows JavaScript to be non-blocking. It continuously monitors the call stack and the callback queue. When the call stack is empty, it takes the first callback from the queue and executes it, pushing it onto the call stack. This ensures that asynchronous operations don't block the main thread.

  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 compared to callbacks, by using `.then()` to handle successful results and `.catch()` to handle errors.

  7. What is async/await in JavaScript?

    • Answer: `async/await` is syntactic sugar built on top of promises, making asynchronous code easier to read and write. The `async` keyword makes a function return a promise, and `await` pauses execution until a promise resolves (or rejects).

  8. Explain the difference between a synchronous and an asynchronous operation.

    • Answer: Synchronous operations execute one after another in a sequential manner. Asynchronous operations execute concurrently and do not block the execution of other operations. Asynchronous operations often involve callbacks, promises, or async/await to handle the result once it's available.

  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. It's a tree-like representation of the page's elements.

  10. How do you manipulate the DOM using JavaScript?

    • Answer: You can manipulate the DOM using JavaScript methods like `getElementById`, `querySelector`, `querySelectorAll`, and various methods for changing element properties (e.g., `innerHTML`, `textContent`, `style`, `classList`). You can also add, remove, and move elements in the DOM tree.

  11. What is event delegation?

    • Answer: Event delegation is a technique where you attach an event listener to a parent element instead of individual child elements. This improves performance, especially when dealing with a large number of child elements, because you only need to manage one event listener. The event listener checks the event's target to determine which child element triggered the event.

  12. What are some common JavaScript frameworks or libraries?

    • Answer: Popular JavaScript frameworks and libraries include React, Angular, Vue.js, jQuery, and many others. Each has its strengths and weaknesses, suitable for different types of projects and development styles.

  13. Explain the concept of a virtual DOM.

    • Answer: The virtual DOM is a lightweight in-memory representation of the real DOM. Frameworks like React use it to efficiently update the actual DOM. When changes occur, the virtual DOM is updated first, and then a diffing algorithm determines the minimal changes needed in the real DOM, minimizing browser repaints and improving performance.

  14. What is AJAX?

    • Answer: AJAX (Asynchronous JavaScript and XML) is a technique for updating parts of a web page without reloading the whole page. It uses JavaScript and the `XMLHttpRequest` object (or the `fetch` API) to send asynchronous requests to a server and receive data, allowing for dynamic updates to the user interface.

  15. What is RESTful API?

    • Answer: A RESTful API (Representational State Transfer Application Programming Interface) is an architectural style for building web services. It uses HTTP methods (GET, POST, PUT, DELETE) to perform actions on resources identified by URLs. RESTful APIs are widely used for building web applications and mobile applications that interact with backend servers.

  16. Explain the concept of HTTP methods (GET, POST, PUT, DELETE).

    • Answer: GET retrieves data from a server. POST submits data to be processed to a server. PUT updates existing data on the server. DELETE removes data from the server.

  17. What is JSON?

    • Answer: JSON (JavaScript Object Notation) is a lightweight data-interchange format. It's easy for humans to read and write, and easy for machines to parse and generate. It's commonly used for transmitting data between a web server and a web application.

  18. What is a single-page application (SPA)?

    • Answer: A single-page application loads a single HTML page and dynamically updates the content as the user interacts with it, without requiring full page reloads. This provides a more fluid and responsive user experience.

  19. What are web components?

    • Answer: Web components are reusable custom HTML elements that encapsulate their own functionality, styling, and behavior. They are built using standard web technologies (HTML, CSS, and JavaScript).

  20. What is the difference between inline, internal, and external CSS?

    • Answer: Inline CSS is applied directly within HTML elements using the `style` attribute. Internal CSS is placed within the `