Node.js Query String

Node.js Query String: URL Parameter Parsing & Serialization

The node:querystring module and modern URLSearchParams web standard API provide utilities for parsing and formatting URL query strings into JavaScript key-value objects.

Query String Encoding & Decoding Pipeline

flowchart LR
    A["Raw String: 'name=Alex%20Smith&role=dev&skills=js&skills=node'"]
    -->|"URLSearchParams / querystring.parse()"| B["JS Object: { name: 'Alex Smith', role: 'dev', skills: ['js', 'node'] }"]

Practical Code Example

import querystring from 'node:querystring';

const rawQueryString = 'name=John%20Doe&age=30&interests=coding&interests=crypto';

// 1. Modern WHATWG URLSearchParams Approach (Recommended)
const searchParams = new URLSearchParams(rawQueryString);
console.log('Name:', searchParams.get('name'));              // 'John Doe'
console.log('All Interests:', searchParams.getAll('interests')); // ['coding', 'crypto']

// 2. Legacy querystring module parsing
const parsedObj = querystring.parse(rawQueryString);
console.log('Parsed Object:', parsedObj);

// 3. Serializing JavaScript Objects into Query Strings
const filterCriteria = {
    search: 'Node.js Security',
    page: 1,
    tags: ['backend', 'tutorial']
};

const encodedQuery = querystring.stringify(filterCriteria);
console.log('Encoded Query String:', encodedQuery);
// 'search=Node.js%20Security&page=1&tags=backend&tags=tutorial'

Best Practices & Gotchas

• Prefer URLSearchParams Web Standard: The legacy querystring module is considered legacy; use the standard URLSearchParams API for cross-environment compatibility.
• Handle Array Parameters: Understand that duplicate query keys (e.g. tag=a&tag=b) resolve into arrays when parsed.
• Sanitize Encoded Inputs: Decoding query strings containing user input should be validated to avoid Injection attacks.

Self-Check Challenge

Parse the string 'category=books&price_max=50' into a URLSearchParams instance and output the category value.