Express.js Handling Query Strings

Query strings are a common way to send data to the server in the URL, usually in the form of key-value pairs. In Express.js, query strings are handled through req.query, allowing you to access and manipulate the data sent as part of the URL.

 

Key Features of Query Strings

• Data Transmission: Query strings are often used for filtering, searching, or passing small amounts of data via the URL.
• Accessing Data: Query string values are available through req.query as an object.
• Flexible Parameter Passing: You can send multiple parameters in a query string.

 

Steps to Handle Query Strings 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 Query String Handling
Create a file called app.js and define routes to handle query strings:

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

// Route with query string parameters
app.get('/search', (req, res) => {
    const query = req.query.q || 'No query provided';
    res.send(`Search results for: ${query}`);
});

// Route to handle multiple query parameters
app.get('/filter', (req, res) => {
    const category = req.query.category || 'All';
    const sort = req.query.sort || 'ascending';
    res.send(`Filter results - Category: ${category}, Sort order: ${sort}`);
});

// Route with optional query parameters
app.get('/page', (req, res) => {
    const page = req.query.page || 1;
    const limit = req.query.limit || 10;
    res.send(`Displaying page ${page} with ${limit} results per page.`);
});

// 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 query string routes:

• http://localhost:3000/search?q=express – Displays "Search results for: express"
• http://localhost:3000/filter?category=electronics&sort=descending – Displays "Filter results - Category: electronics, Sort order: descending"
• http://localhost:3000/page?page=2&limit=5 – Displays "Displaying page 2 with 5 results per page"
• http://localhost:3000/page – Displays "Displaying page 1 with 10 results per page" (using default values).

Accessing Query String Parameters
Query parameters are accessed through req.query as an object:

const query = req.query.q;  // Accesses the 'q' parameter
const category = req.query.category;  // Accesses the 'category' parameter

Handling Missing Query Parameters
If a query parameter is not present in the URL, you can provide a default value by using a logical OR (||) operator:

const page = req.query.page || 1;  // Default to 1 if 'page' is missing
const sort = req.query.sort || 'ascending';  // Default to 'ascending' if 'sort' is missing

 

Summary

Express.js makes it easy to handle query strings through req.query. This allows you to retrieve data passed in the URL in key-value format, making it useful for filtering, sorting, or searching. You can access query parameters dynamically, provide default values for missing parameters, and handle multiple query parameters in a flexible manner to meet your application's needs.