Front End Interview: Javascript
Published: 2024-06-24 07:16:12

### 1. What are the differences between `.then()` and `async/await` in handling asynchronous operations in JavaScript?
Use `.then()` for promise chaining and `async/await` to make asynchronous code look synchronous, improving readability and error handling.

### 2. What are the lifecycle methods in React components, and how are they used?
Lifecycle methods like `componentDidMount()` and hooks like `useEffect()` are used for performing side effects such as data fetching after the initial render.

### 3. How does CORS enhance security, and how can it be managed?
CORS restricts web applications from requesting resources from different domains; manage it by configuring the server to include appropriate CORS headers like `Access-Control-Allow-Origin`.

### 4. When should you use `useState` vs. `useReducer` in React?
Use `useState` for simple state logic and `useReducer` for complex state logic that involves multiple sub-values or when the next state depends on the previous one.

### 5. What is the virtual DOM, and how does it work in React?
The virtual DOM is a lightweight copy of the real DOM, used by React to optimize rendering by updating only changed elements.

### 6. How do you handle state management in a React application?
Use state management libraries like Redux or Context API for managing global state across components.

### 7. What is the purpose of prop drilling, and how can it be avoided?
Prop drilling passes data through multiple levels of components; avoid it by using Context API or state management libraries.

### 8. Explain the concept of higher-order components (HOCs) in React.
HOCs are functions that take a component and return a new component, enhancing it with additional functionality.

### 9. What are CSS preprocessors, and why are they useful?
CSS preprocessors like Sass and Less extend CSS with variables, nesting, and mixins, making stylesheets more maintainable.

### 10. How do you optimize the performance of a React application?
Optimize performance by using techniques like code splitting, lazy loading, memoization, and avoiding unnecessary re-renders.

### 11. What are Webpack and Babel, and how are they used in front-end development?
Webpack is a module bundler, and Babel is a JavaScript compiler; both are used to transform and bundle code for deployment.

### 12. Explain the box model in CSS and its components.
The box model consists of content, padding, border, and margin, defining the layout and spacing of elements.

### 13. How do media queries work in CSS for responsive design?
Media queries apply styles based on device characteristics like width and height, enabling responsive design.

### 14. What are the different types of positioning in CSS?
Positioning types include static, relative, absolute, fixed, and sticky, each affecting element layout differently.

### 15. How do you create a grid layout using CSS Grid?
Use CSS Grid properties like `grid-template-columns` and `grid-template-rows` to define a grid layout.

### 16. What is flexbox and its key properties?
Flexbox is a layout model for distributing space along a single row or column; key properties include `flex-direction`, `justify-content`, and `align-items`.

### 17. What are the differences between `localStorage`, `sessionStorage`, and cookies?
`localStorage` and `sessionStorage` store data in the browser with different lifespans, while cookies store data that can be sent to the server.

### 18. How do you implement form validation in JavaScript?
Implement form validation using HTML5 validation attributes and JavaScript for custom validation logic.

### 19. What is the purpose of a polyfill in web development?
Polyfills add support for modern JavaScript features in older browsers that do not natively support them.

### 20. How do you manage dependencies in a front-end project?
Manage dependencies using package managers like npm or Yarn, and define them in `package.json`.