Install & Compatibility
Where this runs
tested against v? · npm install
Install × environment matrix
Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux
muslnode 18–226 runs
build_error
glibcnode 18–226 runs
build_error
Code
Verified usage
Verified import paths — ran on the pinned version, not inferred.
compression
✓ import compression from 'compression';
✗ import { compression } from 'compression';
The package primarily uses CommonJS `module.exports = compression`, which ES modules typically import as a default export.
compression
✓ const compression = require('compression');
Standard CommonJS import pattern, as shown in the package documentation.
Demonstrates setting up an Express server with `compression` middleware, including basic configuration options like compression level, custom filtering, and size threshold. It also provides curl commands to test different compression scenarios.
import express from 'express';
import compression from 'compression';
import { createServer } from 'http';
const app = express();
// Apply compression middleware globally or to specific routes
app.use(compression({
level: 6, // Default compression level (0-9)
filter: (req, res) => {
if (req.headers['x-no-compression']) {
// Example: don't compress responses with 'x-no-compression' header
return false;
}
// Fallback to the default filter function which checks Content-Type
return compression.filter(req, res);
},
threshold: 0 // Compress all responses regardless of size (in bytes)
}));
app.get('/', (req, res) => {
// A large enough response to demonstrate compression effectiveness
const data = Array(5000).fill('This is some highly repetitive text that will compress extremely well.').join('');
res.send(`<h1>Hello Compressed World!</h1><p>${data}</p>`);
});
const PORT = process.env.PORT || 3000;
const server = createServer(app);
server.listen(PORT, () => {
console.log(`Server listening on http://localhost:${PORT}`);
console.log('Test with cURL:');
console.log(` curl -H "Accept-Encoding: gzip" http://localhost:${PORT}/ -I`);
console.log(` curl -H "Accept-Encoding: br" http://localhost:${PORT}/ -I`);
console.log(` curl http://localhost:${PORT}/ -I`);
console.log(` curl -H "x-no-compression: true" -H "Accept-Encoding: gzip" http://localhost:${PORT}/ -I`);
});
Debug
Known issues
gotchaBrotli compression (br) is only supported in Node.js versions v11.7.0 and v10.16.0 or newer. On older Node.js environments, Brotli will not be available even if specified.fixUpgrade Node.js to a version that supports Brotli (e.g., 10.16.0+, 11.7.0+, 12.0.0+).
affects: <10.16.0 || <11.7.0
gotchaThe middleware will explicitly skip compression for responses that include a `Cache-Control` header with the `no-transform` directive, as compressing would alter the body contrary to the directive.fixEnsure that if you desire compression, your application does not send `Cache-Control: no-transform` headers. If you need `no-transform` for caching, consider if compression is appropriate for those specific responses.
affects: >=1.0.0
gotchaMiddleware order matters in Express. If `compression` is placed after routes or other middleware that send response headers, it will be unable to compress the response, leading to the 'Cannot set headers after they are sent' error.fixEnsure `app.use(compression())` is placed early in your middleware chain, preferably before route definitions or any middleware that might send headers (e.g., `res.send()`, `res.json()`, `res.end()`).
affects: >=1.0.0
Errors
Common errors & fixes
Error: Cannot find module 'compression'
The 'compression' package has not been installed or is not accessible in the current project.
fixRun `npm install compression` or `yarn add compression` in your project directory.
Error: Can't set headers after they are sent to the client
The `compression` middleware attempted to modify response headers after they had already been sent to the client, typically because another middleware or route handler completed the response before `compression` could act.
fixEnsure `compression()` middleware is applied early in your Express application's middleware stack, ideally before route definitions or any middleware that finalizes the response.
Response content is not compressed (e.g., `Content-Encoding` header missing or not expected encoding)
Several reasons can prevent compression: the client did not send an `Accept-Encoding` header supporting the available algorithms, the response's `Content-Type` was not deemed compressible by the `filter` function, the `Cache-Control: no-transform` header was present, or the response size was below the `threshold`.
fixCheck the client's `Accept-Encoding` header. Verify your `filter` function's logic. Ensure no `Cache-Control: no-transform` header is sent. Adjust the `threshold` option to `0` to compress all responses if desired, or a small number like `1024` to compress small responses too.
Audit
Dependencies
expressoptionalCommonly used with Express.js as middleware; while not a direct runtime dependency of the package itself, it's the primary use case.