https://github.com/codewitheshayoutube/js-interview-qs-

https://github.com/codewitheshayoutube/js-interview-qs-

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• Host: GitHub
• URL: https://github.com/codewitheshayoutube/js-interview-qs-
• Owner: codewithEshaYoutube
• Created: 2024-11-01T05:24:33.000Z (over 1 year ago)
• Default Branch: main
• Last Pushed: 2024-11-01T05:34:46.000Z (over 1 year ago)
• Last Synced: 2025-05-26T23:42:21.448Z (about 1 year ago)
• Size: 2.93 KB
• Stars: 2
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

          
# 🌟 Top 30 JavaScript Interview Questions for FAANG Companies 🌟

## 1. What is JavaScript?

- A high-level, interpreted programming language primarily used for web development.

---

## 2. Explain the difference between `var`, `let`, and `const`.

- **`var`**: Function-scoped or globally scoped, can be re-declared.

- **`let`**: Block-scoped, cannot be re-declared in the same block.

- **`const`**: Block-scoped, must be initialized at declaration, cannot be re-assigned.

---

## 3. What are closures in JavaScript?

- Functions that retain access to their lexical scope even when the function is executed outside that scope.

---

## 4. What is the event loop in JavaScript?

- A mechanism that handles asynchronous callbacks, allowing non-blocking I/O operations.

---

## 5. Explain the concept of hoisting.

- Variable and function declarations are moved to the top of their containing scope during compilation.

---

## 6. What are promises in JavaScript?

- Objects that represent the eventual completion (or failure) of an asynchronous operation and its resulting value.

---

## 7. How do you handle errors in JavaScript?

- Using `try...catch` statements, and promise `.catch()` for handling asynchronous errors.

---

## 8. What is the difference between synchronous and asynchronous code?

- **Synchronous**: Runs sequentially.

- **Asynchronous**: Allows other operations to run before completing a task.

---

## 9. Describe the `this` keyword in JavaScript.

- Refers to the object from which a function was called, context-dependent based on how a function is invoked.

---

## 10. What are arrow functions?

- Shorter syntax for writing functions, automatically binding `this` to the surrounding context.

---

## 11. What is the purpose of `bind()`, `call()`, and `apply()`?

- Methods to set the `this` context for functions:

  - **`bind()`**: Returns a new function with bound `this`.

  - **`call()`**: Invokes a function with a specified `this` value.

  - **`apply()`**: Similar to `call()`, but accepts an array of arguments.

---

## 12. Explain the concept of the prototype chain.

- Mechanism by which JavaScript objects inherit properties and methods from other objects through their prototype.

---

## 13. What are higher-order functions?

- Functions that take other functions as arguments or return them as output.

---

## 14. What is the difference between `==` and `===`?

- **`==`**: Abstract equality (coerces types).

- **`===`**: Strict equality (no type coercion).

---

## 15. Describe the `fetch` API.

- A modern interface for making HTTP requests, returning promises that resolve to the response of the request.

---

## 16. What is the significance of the `async` and `await` keywords?

- Used to work with promises in a more synchronous manner, making asynchronous code easier to read and write.

---

## 17. Explain destructuring assignment.

- A syntax that allows unpacking values from arrays or properties from objects into distinct variables.

---

## 18. What is the spread operator?

- A syntax (`...`) that expands an iterable into more elements, useful for array and object manipulation.

---

## 19. How does garbage collection work in JavaScript?

- Automatic memory management process that frees up memory by removing objects no longer in use.

---

## 20. What is a JavaScript module?

- A file or script that exports functions, objects, or variables, allowing code reuse and modularity.

---

## 21. Explain the concept of immutability.

- The state of an object cannot be modified after it is created, often used with libraries like Immutable.js.

---

## 22. What are template literals?

- String literals that allow embedded expressions, multi-line strings, and improved readability.

---

## 23. How do you optimize JavaScript performance?

- Techniques include minimizing DOM manipulation, using debouncing/throttling for events, and optimizing loops.

---

## 24. What are service workers?

- Scripts that run in the background, separate from web pages, enabling features like caching and background sync.

---

## 25. Explain the difference between `setTimeout` and `setInterval`.

- **`setTimeout`**: Executes a function once after a delay.

- **`setInterval`**: Repeatedly executes a function at specified intervals.

---

## 26. How do you retrieve data using a callback function in JavaScript?

### Example Code:

```html

// Simulated API call

function fetchUserData(callback) {

    setTimeout(() => {

        const userData = {

            name: "John Doe",

            age: 30,

            email: "john.doe@example.com"

        };

        // Call the callback function with the retrieved data

        callback(userData);

    }, 1000); // Simulates a 1-second delay

}

// Callback function to process user data

function processUserData(data) {

    console.log("User Data Retrieved:");

    console.log(`Name: ${data.name}`);

    console.log(`Age: ${data.age}`);

    console.log(`Email: ${data.email}`);

}

// Retrieve user data and process it

fetchUserData(processUserData);