javascript 45 lines · 9 steps

Tuning Express response compression

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

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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

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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.

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