javascript 45 lines · 9 steps

Tuning Express response compression

A custom filter and compression options decide which Express responses get gzipped and how aggressively.

Explained by highlit
Express Intermediate compression middleware http performance streaming
1const express = require('express');
2const compression = require('compression');
3const zlib = require('zlib');
4 
5const app = express();
6 
7function shouldCompress(req, res) {
8 if (req.headers['x-no-compression']) {
9 return false;
10 }
11 
12 const type = res.getHeader('Content-Type') || '';
13 if (/^(image|video|audio)\//.test(type) || /\bgzip\b/.test(type)) {
14 return false;
15 }
16 
17 return compression.filter(req, res);
18}
19 
20app.use(
21 compression({
22 filter: shouldCompress,
23 threshold: 1024,
24 level: zlib.constants.Z_BEST_SPEED,
25 memLevel: 8,
26 })
27);
28 
29app.get('/api/report', (req, res) => {
30 const rows = Array.from({ length: 5000 }, (_, i) => ({
31 id: i,
32 label: `item-${i}`,
33 value: Math.round(Math.random() * 1000),
34 }));
35 
36 res.type('application/json');
37 res.json({ generatedAt: new Date().toISOString(), rows });
38});
39 
40app.get('/api/ping', (req, res) => {
41 res.set('x-no-compression', '1');
42 res.type('text/plain').send('pong');
43});
44 
45module.exports = app;
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1A custom filter lets you skip compression for already-compressed or tiny payloads instead of wasting CPU on them.
  2. 2Compression options like level and threshold trade CPU time against bandwidth savings.
  3. 3Requests can opt out of compression by signalling intent through a header your filter checks.

Related explainers

javascript 
const RESERVED_SLUGS = new Set(['new', 'edit', 'admin', 'api']);
 
function slugify(title) {
  return title

Generating URL-safe unique slugs

string-normalization regex deduplication
Intermediate 9 steps
go 
package api
 
func RegisterRoutes(r *gin.Engine, deps *Dependencies) {
	r.GET("/health", func(c *gin.Context) {

Layering route groups and middleware in Gin

routing middleware authentication
Intermediate 8 steps
java 
@Component
@Order(20)
public class ProductSearchIndexRunner implements ApplicationRunner {
 

Rebuilding a search index at Spring startup

startup-hook batching streaming
Intermediate 8 steps
javascript 
class EventEmitter {
  constructor() {
    this.listeners = new Map();
  }

Building an EventEmitter in JavaScript

pub-sub closures map
Intermediate 7 steps
php 
<?php
 
function uploadDocument(string $endpoint, string $filePath, array $meta): array
{

Uploading a file with cURL in PHP

curl file-upload http
Intermediate 8 steps
javascript 
import { NextResponse } from 'next/server'
 
const UPSTREAM = 'https://api.exchangerate.host/latest'
 

A cached exchange-rate proxy in Next.js

route-handler caching revalidation
Intermediate 7 steps

Share this explainer

Here's the card — post it anywhere.

Tuning Express response compression — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code