Relative vs absolute URL resolution in Node.js - Performance Comparison

Performance: Relative vs absolute URL resolution

MEDIUM IMPACT

This concept affects how URLs are resolved in web requests, impacting network request efficiency and caching behavior.

Resolving URLs for fetching resources in a Node.js web app

Node.js

const baseUrl = 'https://example.com/assets/';
const imageUrl = new URL('data.json', baseUrl).href;
fetch(imageUrl).then(res => res.json());

Relative URLs reuse the current domain context, reducing DNS lookups and improving cache hits.

📈 Performance GainSaves DNS lookup time, reducing load time by ~50-100ms per resource

Resolving URLs for fetching resources in a Node.js web app

Node.js

const imageUrl = 'https://example.com/assets/data.json';
fetch(imageUrl).then(res => res.json());

Using absolute URLs causes repeated DNS lookups and prevents efficient caching when the base URL is known.

📉 Performance CostAdds extra DNS lookup per request, increasing load time by ~50-100ms per resource

Performance Comparison

Pattern	DNS Lookups	Cache Efficiency	Network Overhead	Verdict
Absolute URL	Multiple per resource	Lower due to domain changes	Higher due to repeated lookups	[X] Bad
Relative URL	Single or none	Higher due to consistent domain	Lower network overhead	[OK] Good

Rendering Pipeline

URL resolution happens before network requests; absolute URLs require full domain resolution, while relative URLs resolve locally based on the current context.

→Network Request Preparation

→DNS Lookup

→Cache Lookup

⚠️ BottleneckDNS Lookup stage is most expensive when using absolute URLs repeatedly.

Core Web Vital Affected

LCP

This concept affects how URLs are resolved in web requests, impacting network request efficiency and caching behavior.

Optimization Tips

1Use relative URLs for resources on the same domain to reduce DNS lookups.

2Avoid absolute URLs unless fetching from a different domain or CDN.

3Consistent URL resolution improves caching and reduces network overhead.

Performance Quiz - 3 Questions

Which URL type reduces DNS lookups when fetching multiple resources from the same domain?

A Absolute URL

B Relative URL

C Data URL

D Protocol-relative URL

DevTools: Network

How to check: Open DevTools > Network tab, reload page, and observe DNS lookup timings and request URLs.

What to look for: Look for repeated DNS lookups and longer request times for absolute URLs versus faster requests for relative URLs.