MERN Stack Interview Questions and Answers- Part 5

Answer:

To ensure consistent code style in Node.js, you can use tools like:

1. ESLint: A popular linter that helps identify and fix code style and syntax issues. It supports various plugins and configurations to enforce coding standards.
2. Prettier: A code formatter that automatically formats code according to predefined rules, ensuring consistent formatting across the project.
3. TSLint (for TypeScript projects): Similar to ESLint but tailored for TypeScript, it enforces coding standards and identifies issues in TypeScript code.
4. Standard.js: A minimalistic coding style guide and linter for JavaScript that promotes consistent and readable code.
5. JSHint: A linter that checks JavaScript code for potential errors and style issues, offering options to customize linting rules.

Answer:

Node.js uses an asynchronous, non-blocking architecture. It delegates I/O operations to the operating system, allowing the application to continue executing other tasks without waiting for the I/O operation to complete. This prevents blocking and ensures efficient resource utilization.

Answer:

Here’s a simple example of creating a server in Node.js that returns “Hello World” when accessed through a web browser:

“`javascript

const http = require(‘http’);

const server = http.createServer((req, res) => {

res.writeHead(200, { ‘Content-Type’: ‘text/plain’ });

res.end(‘Hello World\n’);

});

server.listen(3000, ‘127.0.0.1’, () => {

console.log(‘Server is listening on port 3000’);

});

“`

Answer:

In Node.js, the `fork` method is used to create child processes. These child processes are essentially separate instances of the Node.js runtime. Each child process has its own memory space, event loop, and can communicate with the parent process through inter-process communication (IPC).

Answer:

A first-class function in JavaScript refers to the ability to treat functions as first-class citizens. This means functions can be passed as arguments to other functions, returned from functions, and assigned to variables. They can also be stored in data structures like arrays or objects.

Answer:

Node.js is an open-source runtime environment that allows you to execute JavaScript code on the server-side. It uses an event-driven, non-blocking I/O model, which makes it efficient and suitable for building scalable network applications.

Answer:

You can manage packages in your Node.js project using `npm` (Node Package Manager). You create a `package.json` file to define your project’s dependencies and metadata. You can then install packages using `npm install`, and it will fetch the required packages and store them in the `node_modules` directory.

Answer:

Node.js is known for its non-blocking, event-driven architecture, which makes it highly efficient for handling a large number of concurrent connections. It’s particularly well-suited for building real-time applications, APIs, and microservices due to its lightweight nature and the ability to share code between the server and the client.

Answer:

Control flow modules in Node.js like `async` or `Promise` libraries help manage the execution order of asynchronous functions. They provide mechanisms to handle callbacks, promises, or async/await syntax to ensure that functions are executed in the desired sequence.

Answer:

Common timing features in Node.js include:

• `setTimeout`: Executes a function after a specified delay.
• `setInterval`: Repeatedly executes a function with a given time interval.
• `process.nextTick`: Schedules a function to be executed in the next iteration of the event loop.
• `setImmediate`: Schedules a function to be executed in the current iteration of the event loop.

Answer:

Promises offer several advantages over callbacks, including:

• Improved code readability with chaining and error handling.
• Avoiding callback hell and achieving better code organization.
• Enhanced error handling through the `.catch()` method.
• Better support for asynchronous operations that require multiple steps.

Answer:

There are several ways to style React components:

• Inline Styles: Apply styles directly to JSX elements using the `style` attribute.
• CSS Modules: Create a separate CSS file for each component and import it into the component.
• Styled Components: Use a library like Styled Components to write CSS-in-JS directly within your components.
• CSS-in-JS Libraries: Other libraries like Emotion, Radium, etc., offer similar functionality to Styled Components.
• Global Styles: Apply global styles using traditional CSS files or libraries like `styled-components`.

Answer:

Some techniques to optimize React app performance include:

• Memorization: Memoize functions and components to prevent unnecessary re-renders.
• Virtualization: Use libraries like `react-virtualized` to efficiently render large lists or grids.
• Code Splitting: Split your code into smaller chunks and load them only when needed.
• Lazy Loading: Load components lazily using React’s `lazy()` and `Suspense`.
• Optimize Renders: Use shouldComponentUpdate, PureComponent, or React.memo to prevent unnecessary renders.
• Minimize Re-renders: Use `useMemo` and `useCallback` hooks to optimize re-renders.
• Avoid Unnecessary State Updates: Use `setState` carefully and avoid unnecessary re-renders.
• Server-Side Rendering (SSR): Render components on the server side for faster initial load.

Answer:

Data can be passed between React components through props (short for properties). Props are passed from parent components to child components, allowing the child components to access and use the data.

Answer:

In the class component lifecycle, the phases include:

• Mounting: When the component is being created and inserted into the DOM.
• Updating: When the component’s state or props change and it needs to re-render.
• Unmounting: When the component is being removed from the DOM.

With the introduction of React Hooks, the component lifecycle phases are managed differently.

Answer:

Props are inputs that a React component receives from its parent component. They are read-only and help to pass data down the component tree.

State is a data structure that holds the internal state of a component. It can be changed and updated using the `setState` method. Changes in state trigger re-renders.

Answer:

Side effects are operations that can be performed within React components, often involving interactions with the outside world. There are two types of side effects in React:

• Lifecycle Side Effects: These occur during the various phases of a component’s lifecycle (e.g., `componentDidMount`, `componentDidUpdate`, `componentWillUnmount`).
• Hooks Side Effects: These are managed using hooks like `useEffect`, allowing you to perform side effects within functional components.

Answer:

Error boundaries are React components that catch and handle errors during rendering, ensuring that errors in one component do not break the entire application. They are defined using the `componentDidCatch` lifecycle method in class components or `ErrorBoundary` components in functional components.

Answer:

Some important rules for using React Hooks include:

• Only call hooks at the top level of functional components or custom hooks.
• Don’t call hooks inside loops, conditions, or nested functions.
• Use hooks consistently in the same order in every render.

Answer:

The `useEffect` hook is used to manage side effects in functional components. It replaces lifecycle methods like `componentDidMount`, `componentDidUpdate`, and `componentWillUnmount`. It allows you to perform actions after rendering, like data fetching, subscriptions, or DOM manipulations.