Q1. What are route parameters in Express?
Route parameters are named URL segments used to capture values at specific positions in the URL. They are defined with a colon prefix. Example: /users/:userId/books/:bookId. The values are stored in req.params: { userId: '123', bookId: '456' }.
Q2. How do you access route parameters?
Through the req.params object. For a route defined as app.get('/products/:id', ...), you access the id with req.params.id. If you have multiple parameters, they all become properties of req.params.
Q3. What are query parameters and how do you access them?
Query parameters come after ? in the URL (e.g., /search?q=express&page=2). They are accessed via req.query. For the example, req.query gives { q: 'express', page: '2' }. Query parameters are optional and used for filtering, sorting, or pagination.
Q4. Can route parameters be optional?
In Express, route parameters are required by default. To make them optional, you need to use a regular expression or define multiple routes. Alternatively, you can use query parameters for optional values, or use app.all() with conditional logic.
Q5. How do you build dynamic URLs in Express?
You combine static parts with route parameters. For example, /posts/:postId/comments/:commentId. This creates a hierarchical structure. You can also use regular expressions in route paths for more complex matching, like /user/:id(\d+) to match only numeric IDs.