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Express.js
Node.js
Web Development
JavaScript
Query String Variables

How to get GET (query string) variables in Express.js on Node.js?

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Introduction

In Express.js, query string parameters from GET requests are available on req.query, a parsed object where each key maps to its value from the URL. For a request to /search?q=nodejs&page=2, req.query.q returns "nodejs" and req.query.page returns "2". Express parses the query string automatically using the qs library, so no additional middleware is needed.

Basic Usage

javascript
1const express = require('express');
2const app = express();
3
4app.get('/search', (req, res) => {
5    const query = req.query.q;
6    const page = req.query.page;
7    res.json({ query, page });
8});
9
10app.listen(3000);
11
12// GET /search?q=nodejs&page=2
13// Response: { "query": "nodejs", "page": "2" }

All req.query values are strings. If the URL has no query string, req.query is an empty object {}.

Accessing Multiple Parameters

javascript
1app.get('/api/products', (req, res) => {
2    const { category, minPrice, maxPrice, sort, order } = req.query;
3
4    console.log(category);  // "electronics"
5    console.log(minPrice);  // "100"
6    console.log(maxPrice);  // "500"
7    console.log(sort);      // "price"
8    console.log(order);     // "asc"
9
10    res.json({ category, minPrice, maxPrice, sort, order });
11});
12
13// GET /api/products?category=electronics&minPrice=100&maxPrice=500&sort=price&order=asc

Use destructuring for clean access to multiple parameters.

Type Conversion

Query string values are always strings. Convert them explicitly:

javascript
1app.get('/api/items', (req, res) => {
2    // String to number
3    const page = parseInt(req.query.page, 10) || 1;
4    const limit = parseInt(req.query.limit, 10) || 20;
5
6    // String to boolean
7    const active = req.query.active === 'true';
8
9    // String to float
10    const lat = parseFloat(req.query.lat) || 0;
11    const lng = parseFloat(req.query.lng) || 0;
12
13    res.json({ page, limit, active, lat, lng });
14});
15
16// GET /api/items?page=3&limit=50&active=true&lat=40.7128&lng=-74.0060

Default Values

javascript
1app.get('/api/users', (req, res) => {
2    const page = parseInt(req.query.page, 10) || 1;
3    const limit = Math.min(parseInt(req.query.limit, 10) || 20, 100);
4    const sort = req.query.sort || 'createdAt';
5    const order = req.query.order || 'desc';
6    const search = req.query.q || '';
7
8    // Use defaults when parameters are missing
9    res.json({ page, limit, sort, order, search });
10});
11
12// GET /api/users           → { page: 1, limit: 20, sort: "createdAt", ... }
13// GET /api/users?page=3    → { page: 3, limit: 20, sort: "createdAt", ... }

Arrays in Query Strings

Express supports arrays via repeated keys or bracket notation:

javascript
1app.get('/api/filter', (req, res) => {
2    const tags = req.query.tags;
3    console.log(tags);
4    res.json({ tags });
5});
6
7// GET /api/filter?tags=node&tags=express&tags=mongodb
8// tags = ["node", "express", "mongodb"]
9
10// GET /api/filter?tags[]=node&tags[]=express
11// tags = ["node", "express"]
12
13// GET /api/filter?tags=node
14// tags = "node" (string, not array, only one value!)

When only one value is provided, req.query.tags is a string, not an array. Normalize it:

javascript
const tags = [].concat(req.query.tags || []);
// Always an array, even with 0 or 1 values

Nested Objects

Express uses the qs library by default, which supports nested objects:

javascript
1app.get('/api/search', (req, res) => {
2    const filters = req.query.filter;
3    console.log(filters);
4    res.json({ filters });
5});
6
7// GET /api/search?filter[status]=active&filter[role]=admin
8// filters = { status: "active", role: "admin" }

req.query vs req.params vs req.body

javascript
1// req.params: URL path parameters (from route definition)
2app.get('/users/:id', (req, res) => {
3    req.params.id;  // "42" from /users/42
4});
5
6// req.query: query string parameters (after ?)
7app.get('/users', (req, res) => {
8    req.query.page;  // "2" from /users?page=2
9});
10
11// req.body: POST/PUT request body (needs middleware)
12app.post('/users', express.json(), (req, res) => {
13    req.body.name;  // From JSON body: { "name": "Alice" }
14});

Validation with express-validator

javascript
1const { query, validationResult } = require('express-validator');
2
3app.get('/api/search',
4    query('q').isString().trim().notEmpty().withMessage('Search query required'),
5    query('page').optional().isInt({ min: 1 }).toInt(),
6    query('limit').optional().isInt({ min: 1, max: 100 }).toInt(),
7    (req, res) => {
8        const errors = validationResult(req);
9        if (!errors.isEmpty()) {
10            return res.status(400).json({ errors: errors.array() });
11        }
12        const { q, page = 1, limit = 20 } = req.query;
13        res.json({ q, page, limit });
14    }
15);

URL Encoding

Special characters in query strings must be URL-encoded:

javascript
1// Client side
2const searchTerm = 'hello world & more';
3const url = `/search?q=${encodeURIComponent(searchTerm)}`;
4// /search?q=hello%20world%20%26%20more
5
6// Express decodes automatically
7app.get('/search', (req, res) => {
8    console.log(req.query.q);  // "hello world & more"
9});

Common Pitfalls

  • Values are always strings: req.query.page is "2", not 2. Use parseInt() or parseFloat() for numbers, and === 'true' for booleans. Forgetting this causes bugs in comparisons and arithmetic.
  • Missing parameters are undefined: req.query.missing returns undefined, not null or empty string. Use || default or optional chaining req.query.key?.trim().
  • Single value vs array inconsistency: ?tag=one gives a string, ?tag=one&tag=two gives an array. Always normalize with [].concat(req.query.tag || []).
  • Query string size limits: Express defaults to a max query string length of 1000 characters. Override with app.set('query parser', qs => qs.parse(qs, { parameterLimit: 5000 })) if needed.
  • Prototype pollution: The qs parser protects against __proto__ injection by default in modern Express versions, but always validate and sanitize query parameters before using them in database queries.

Summary

  • Use req.query to access GET query string parameters. No middleware needed
  • All values are strings; convert explicitly with parseInt(), parseFloat(), or boolean comparison
  • Provide default values with || default for optional parameters
  • Arrays are supported via repeated keys (?a=1&a=2) or bracket notation (?a[]=1&a[]=2)
  • Use req.params for URL path segments, req.query for query strings, req.body for POST data
  • Validate query parameters with express-validator for production APIs
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