How to Handle Optional Parameters in Express Routes

Table Of Contents

• Problem
• Solution
• Explanation

Problem

You need to create routes that work with optional parameters, like /users and /users/123, or /search and /search/category/electronics without duplicating route definitions.

Solution

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

// Method 1: Optional parameter with ?
app.get('/users/:id?', (req, res) => {
  const userId = req.params.id;
  
  if (userId) {
    // GET /users/123
    res.json({ 
      message: `User details for ID: ${userId}`,
      user: { id: userId, name: 'John Doe' }
    });
  } else {
    // GET /users
    res.json({ 
      message: 'All users',
      users: [
        { id: 1, name: 'John' },
        { id: 2, name: 'Jane' }
      ]
    });
  }
});

// Method 2: Multiple optional parameters
app.get('/search/:query?/:category?', (req, res) => {
  const { query, category } = req.params;
  
  let result = {
    query: query || 'all',
    category: category || 'general',
    results: []
  };
  
  if (query && category) {
    // GET /search/laptop/electronics
    result.results = [`${query} in ${category}`];
  } else if (query) {
    // GET /search/laptop
    result.results = [`${query} in all categories`];
  } else {
    // GET /search
    result.results = ['All items'];
  }
  
  res.json(result);
});

// Method 3: Using regex for complex optional patterns
app.get(/^\/products\/?(\d+)?\/?$/, (req, res) => {
  const productId = req.params[0]; // First capture group
  
  if (productId) {
    res.json({ 
      message: `Product ${productId}`,
      product: { id: productId, name: 'Sample Product' }
    });
  } else {
    res.json({ 
      message: 'All products',
      products: ['Product 1', 'Product 2']
    });
  }
});

// Method 4: Separate routes with shared logic
const handleArticles = (req, res) => {
  const { category, slug } = req.params;
  
  if (category && slug) {
    res.json({ 
      type: 'specific article',
      category,
      slug,
      article: `Article: ${slug} in ${category}`
    });
  } else if (category) {
    res.json({ 
      type: 'category articles',
      category,
      articles: [`Articles in ${category}`]
    });
  } else {
    res.json({ 
      type: 'all articles',
      articles: ['All articles']
    });
  }
};

app.get('/articles', handleArticles);
app.get('/articles/:category', handleArticles);
app.get('/articles/:category/:slug', handleArticles);

// Method 5: Using query parameters as alternative
app.get('/api/posts', (req, res) => {
  const { category, author, limit = 10 } = req.query;
  
  let filters = {};
  if (category) filters.category = category;
  if (author) filters.author = author;
  
  res.json({
    message: 'Posts with optional filters',
    filters,
    limit: parseInt(limit),
    posts: ['Post 1', 'Post 2']
  });
});

app.listen(3000, () => {
  console.log('Server running on port 3000');
});

Example requests:

# Optional parameter routes
curl http://localhost:3000/users          # All users
curl http://localhost:3000/users/123      # Specific user

# Multiple optional parameters  
curl http://localhost:3000/search                    # All items
curl http://localhost:3000/search/laptop             # Search laptop
curl http://localhost:3000/search/laptop/electronics # Search in category

# Query parameters
curl "http://localhost:3000/api/posts?category=tech&author=john&limit=5"

Explanation

Adding ? after a parameter name makes it optional (:id?). The parameter will be undefined if not provided. For multiple optional parameters, each gets its own ?.

Regex routes offer more control but are harder to read. Query parameters (?category=tech) are often better for optional filters since they're more flexible and don't require specific URL patterns. Choose the method that best fits your API design and user experience needs.