Express.js Route Parameters

Route parameters in Express allow you to define dynamic segments in a URL. These parameters are extracted from the URL and passed to the route handler, which can then use them to perform operations like retrieving data from a database. Route parameters are often used for tasks like user profiles, product pages, or filtering results based on user input.

 

Key Features of Route Parameters

• Dynamic Segments: Define dynamic parts in the URL using :parameterName.
• Accessing Parameters: Parameters are accessible through req.params.
• Flexible Routing: You can use parameters in GET, POST, PUT, DELETE routes.

 

Steps to Use Route Parameters in Express.js

Set up a Basic Express Application
If you haven't already, initialize a Node.js project and install Express:

npm init -y
npm install express --save

Create an Express Application with Route Parameters
Create a file called app.js and define routes with parameters:

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

// Route with a single parameter (e.g., user ID)
app.get('/user/:id', (req, res) => {
    const userId = req.params.id;
    res.send(`User ID: ${userId}`);
});

// Route with multiple parameters (e.g., product and category)
app.get('/product/:category/:id', (req, res) => {
    const category = req.params.category;
    const productId = req.params.id;
    res.send(`Category: ${category}, Product ID: ${productId}`);
});

// Route with an optional parameter (e.g., query string)
app.get('/search/:query?', (req, res) => {
    const query = req.params.query || 'No search query provided';
    res.send(`Search Query: ${query}`);
});

// Start the server
app.listen(3000, () => {
    console.log('Server is running on port 3000');
});

Run the Application
Start the server by running:

node app.js

Test the Routes
Open your browser or use tools like Postman to test the following routes:

• http://localhost:3000/user/123 – Displays "User ID: 123"
• http://localhost:3000/product/electronics/456 – Displays "Category: electronics, Product ID: 456"
• http://localhost:3000/search/laptop – Displays "Search Query: laptop"
• http://localhost:3000/search – Displays "Search Query: No search query provided" (optional parameter).

Handling Multiple Parameters
You can define multiple parameters in the URL by separating them with slashes. Each parameter is then accessible via req.params using the parameter name defined in the route.

app.get('/blog/:category/:postId', (req, res) => {
    const category = req.params.category;
    const postId = req.params.postId;
    res.send(`Category: ${category}, Post ID: ${postId}`);
});

Optional Parameters
Express does not natively support optional parameters directly in the route path, but you can handle optional parameters by using query strings or by defining default values within the route handler.

 

Summary

Route parameters in Express allow you to capture dynamic parts of the URL and pass them to route handlers for processing. These parameters can be used in a variety of ways, such as identifying a user, filtering results, or specifying content in a URL. Express provides an easy and powerful way to create dynamic, parameterized routes that are essential for building interactive web applications and APIs.