compression

HTTP response compression middleware for Express — gzip/deflate responses to reduce bandwidth and improve load times.

compression

Express

HTTP response compression middleware for Express — gzip/deflate responses to reduce bandwidth and improve load times.

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Bundle (gzip)

29.5 kB

177.9 kB raw

Install size includes transitive dependencies. Bundle size is gzipped browser payload.

Freshness

The Problem

Serving large JSON API responses and static assets uncompressed wastes bandwidth and slows down clients. Configuring gzip correctly at the application level (vs. a reverse proxy) requires understanding content negotiation and threshold tuning.

What It Does

The compression middleware compresses responses when the client sends an Accept-Encoding: gzip header and the response exceeds the threshold size. It negotiates between gzip and deflate, skips binary formats (images, video), and adds the appropriate Content-Encoding header.

Installation

bash
npm install compression
npm install -D @types/compression

Usage Example

typescript
import express from 'express';
import compression from 'compression';

const app = express();

// Apply to all routes
app.use(compression({
  threshold: 1024, // only compress responses > 1KB
  filter: (req, res) => {
    // Skip compression for already-compressed formats
    if (req.headers['x-no-compression']) return false;
    return compression.filter(req, res);
  },
}));

app.get('/data', (req, res) => {
  res.json({ users: largeUsersArray }); // automatically gzipped
});

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