code official Interview Questions and Answers

0
100 Code Official Interview Questions and Answers

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

    • Answer: `==` performs loose equality comparison, while `===` performs strict equality comparison. Loose equality coerces types before comparison, while strict equality does not. For example, `1 == "1"` is true (loose), but `1 === "1"` is false (strict).

  2. Explain the concept of closures in JavaScript.

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

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

    • Answer: `var` is function-scoped (or globally scoped if not within a function). `let` and `const` are block-scoped. `const` declares a constant value, which cannot be reassigned after initialization. `let` allows reassignment.

  4. 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. However, only the *declarations* are hoisted, not the *initializations*. This means you can use a variable before it's declared, but its value will be `undefined`.

  5. 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, using `.then()` for success and `.catch()` for error handling.

  6. What is async/await?

    • Answer: `async/await` is syntactic sugar built on top of promises. `async` declares an asynchronous function that returns a promise. `await` pauses execution within an `async` function until a promise resolves.

  7. Explain event bubbling and event capturing.

    • Answer: Event bubbling is the propagation of an event up the DOM tree from the target element to its ancestors. Event capturing is the propagation of an event down the DOM tree from the window to the target element. `addEventListener` allows you to specify whether to use capturing or bubbling.

  8. What is the difference between `null` and `undefined` in JavaScript?

    • Answer: `null` is an assignment value, representing the intentional absence of a value. `undefined` means a variable has been declared but has not been assigned a value.

  9. How do you handle errors in JavaScript?

    • Answer: Use `try...catch` blocks to handle errors gracefully. The `try` block contains the code that might throw an error, and the `catch` block handles the error if it occurs. `finally` blocks can contain cleanup code that always executes.

  10. What is JSON?

    • Answer: JSON (JavaScript Object Notation) is a lightweight text-based format for exchanging data. It's often used for communication between a server and a web application.

  11. 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 the `XMLHttpRequest` object (or the `fetch` API) to communicate with the server asynchronously.

  12. Explain the concept of prototypal inheritance in JavaScript.

    • Answer: JavaScript uses prototypal inheritance, where objects inherit properties and methods from other objects (their prototypes). This creates a chain of inheritance, where objects can inherit from other objects, and so on. The prototype chain ends with `Object.prototype`.

  13. What is a callback function?

    • Answer: A callback function is a function passed as an argument to another function. The function receiving the callback then executes the callback at a later time, often after an asynchronous operation completes.

  14. 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.

  15. Explain the difference between a class and an object in JavaScript.

    • Answer: A class is a blueprint for creating objects. An object is an instance of a class. The class defines the properties and methods that the objects will have.

  16. What is the purpose of the `this` keyword in JavaScript?

    • Answer: The `this` keyword refers to the object that is executing the current function. Its value depends on how the function is called (e.g., method invocation, function invocation, etc.).

  17. What are some common JavaScript frameworks or libraries?

    • Answer: Popular frameworks and libraries include React, Angular, Vue.js, jQuery, Node.js (for server-side JavaScript), etc.

  18. What is a module in JavaScript?

    • Answer: A module is a self-contained unit of code that can be imported and used in other modules. This promotes code reusability and organization.

  19. How can you create an array in JavaScript?

    • Answer: You can create an array using array literals (e.g., `const myArray = [1, 2, 3];`) or the `Array` constructor (e.g., `const myArray = new Array(3);`).

Thank you for reading our blog post on 'code official Interview Questions and Answers'.We hope you found it informative and useful.Stay tuned for more insightful content!