Express JS interview Questions Series: The Last Part

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Question 11: How do you handle file uploads in Express.js?

Answer: To handle file uploads in Express.js, you can use middleware like multer. Here's an example:

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const multer = require('multer');
const upload = multer({ dest: 'uploads/' });

app.post('/upload', upload.single('file'), (req, res) => {
  // Process the uploaded file
  res.send('File uploaded successfully');
});

Question 12: How do you implement route parameter validation in Express.js?

Answer: You can use the express-validator middleware to validate route parameters. Here's an example:

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const { body, validationResult } = require('express-validator');

app.post('/users/:id', [
  body('name').notEmpty().isString(),
  body('email').isEmail()
], (req, res) => {
  const errors = validationResult(req);
  if (!errors.isEmpty()) {
    return res.status(400).json({ errors: errors.array() });
  }

  // Process the user data
  res.send('User data validated successfully');
});

Question 13: How do you implement caching in Express.js?

Answer: Caching in Express.js can be implemented using middleware like express-cache-controller. Here's an example:

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const cacheControl = require('express-cache-controller');

app.use(cacheControl({ maxAge: 3600 }));

app.get('/users', (req, res) => {
  // Serve cached response if available
  // Otherwise, generate the response
});

Question 14: How do you handle Cross-Origin Resource Sharing (CORS) in Express.js?

Answer: To handle CORS in Express.js, you can use the cors middleware. Here's an example:

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const cors = require('cors');
app.use(cors());

app.get('/api/data', (req, res) => {
  // Handle the CORS-enabled request
});

Question 15: How do you deploy an Express.js application to a production environment?

Answer: To deploy an Express.js application to a production environment, you can use platforms like Heroku, AWS, or Azure. Here are the general steps involved:

1. Prepare your application for production by optimizing code, configuring environment variables, etc.
2. Choose a hosting platform and follow their deployment instructions.
3. Set up the necessary infrastructure (e.g., servers, databases, CDN) as per your application requirements.
4. Deploy your application using tools like Git, containerization, or deployment scripts provided by the hosting platform.

These interview questions and code snippets should give you a good starting point for understanding Express.js and its usage in web application development. Remember to dive deeper into each topic and explore the vast ecosystem of Express.js to become proficient in using this powerful framework.

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