Query string parsing in Express - Mini Project: Build & Apply

Query String Parsing with Express

📖 Scenario: You are building a simple Express server that reads user preferences sent as query strings in the URL.For example, a user might visit /settings?theme=dark&fontSize=16 to set their theme and font size.

🎯 Goal: Create an Express server that parses query strings from the URL and responds with a JSON object showing the parsed preferences.

📋 What You'll Learn

Create an Express app instance

Set up a GET route at /settings

Parse the query string parameters theme and fontSize

Respond with a JSON object containing theme and fontSize values

💡 Why This Matters

🌍 Real World

Web servers often need to read user preferences or filters from query strings to customize responses.

💼 Career

Understanding query string parsing is essential for backend developers building APIs or web applications with Express.

1

Set up Express app

Create a variable called express that requires the express module. Then create a variable called app by calling express().

Express

const express = require('express');
const app = express();
// Your code here

Need a hint?

Use require('express') to import Express and then call it as a function to create the app.

2

Add GET route for /settings

Add a GET route handler on app for the path '/settings' using app.get('/settings', (req, res) => { }).

Express

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

app.get('/settings', (req, res) => {
  // Your code here
});

Need a hint?

Use app.get to define a route for /settings.

3

Parse query string parameters

Inside the /settings route handler, create two variables: theme and fontSize. Assign them the values from req.query.theme and req.query.fontSize respectively.

Express

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

app.get('/settings', (req, res) => {
  // Extract theme and fontSize from query
  // Your code here
});

Need a hint?

Access query parameters using req.query.

4

Send JSON response with parsed values

Inside the /settings route handler, send a JSON response using res.json() with an object containing theme and fontSize properties.

Express

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

app.get('/settings', (req, res) => {
  const theme = req.query.theme;
  const fontSize = req.query.fontSize;
  // Send JSON response
  // Your code here
});

Need a hint?

Use res.json() to send a JSON response with the parsed query values.