HTTP Servers & APIs

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What is the proper way to handle errors in Express?

javascript

const express = require("express");
const app = express();

app.use(express.json());

app.get("/api/users/:id", (req, res, next) => {
  try {
    const id = req.params.id;
    
    // Validate input
    if (!id || isNaN(id)) {
      return res.status(400).json({ error: "Invalid user ID" });
    }
    
    // Simulate database fetch
    const user = getUser(id); // Might throw
    
    if (!user) {
      return res.status(404).json({ error: "User not found" });
    }
    
    res.json(user);
  } catch (error) {
    // Pass to error handler middleware
    next(error);
  }
});

// Error handling middleware (must be last)
app.use((err, req, res, next) => {
  console.error("Error:", err.message);
  res.status(500).json({ error: "Internal server error" });
});

app.listen(3000);

AThrow errors and let them crash the server.

BUse try/catch and send error responses.

CIgnore errors; they fix themselves.

DUse console.log to display errors.

What is the benefit of using async/await in Express routes?

javascript

app.get("/api/users/:id", (req, res) => {
  getUser(req.params.id, (err, user) => {
    if (err) {
      return res.status(500).json({ error: err.message });
    }
    
    updateUserLastLogin(user.id, (err) => {
      if (err) {
        return res.status(500).json({ error: err.message });
      }
      
      logActivity(user.id, "viewed", () => {
        res.json(user); // Three levels of nesting
      });
    });
  });
});

AMakes code faster.

BMakes code cleaner and easier to handle errors.

CAsync/await is not useful in Express.

DOnly works for GET requests.

What are environment variables and why use them?

javascript

# .env
DATABASE_URL=postgresql://localhost/mydb
API_KEY=secret123
NODE_ENV=development
PORT=3000

AVariables stored in JavaScript files.

BVariables stored outside code for configuration (database URL, API keys, etc.).

CVariables that change based on user input.

DVariables for environment conditions like temperature.

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