${data}
`);\n});\n\nconst PORT = process.env.PORT || 3000;\nconst server = createServer(app);\n\nserver.listen(PORT, () => {\n console.log(`Server listening on http://localhost:${PORT}`);\n console.log('Test with cURL:');\n console.log(` curl -H \"Accept-Encoding: gzip\" http://localhost:${PORT}/ -I`);\n console.log(` curl -H \"Accept-Encoding: br\" http://localhost:${PORT}/ -I`);\n console.log(` curl http://localhost:${PORT}/ -I`);\n console.log(` curl -H \"x-no-compression: true\" -H \"Accept-Encoding: gzip\" http://localhost:${PORT}/ -I`);\n});","lang":"typescript","description":"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."},"warnings":[{"fix":"Upgrade Node.js to a version that supports Brotli (e.g., 10.16.0+, 11.7.0+, 12.0.0+).","message":"Brotli 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.","severity":"gotcha","affected_versions":"<10.16.0 || <11.7.0"},{"fix":"Ensure 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.","message":"The 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.","severity":"gotcha","affected_versions":">=1.0.0"},{"fix":"Ensure `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()`).","message":"Middleware 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.","severity":"gotcha","affected_versions":">=1.0.0"}],"env_vars":null,"last_verified":"2026-04-23T00:00:00.000Z","next_check":"2026-07-22T00:00:00.000Z","problems":[{"fix":"Run `npm install compression` or `yarn add compression` in your project directory.","cause":"The 'compression' package has not been installed or is not accessible in the current project.","error":"Error: Cannot find module 'compression'"},{"fix":"Ensure `compression()` middleware is applied early in your Express application's middleware stack, ideally before route definitions or any middleware that finalizes the response.","cause":"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.","error":"Error: Can't set headers after they are sent to the client"},{"fix":"Check 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.","cause":"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`.","error":"Response content is not compressed (e.g., `Content-Encoding` header missing or not expected encoding)"}],"ecosystem":"npm","meta_description":null,"install_score":null,"install_tag":null,"quickstart_score":null,"quickstart_tag":null}