Error: EMFILE: too many open files when reading or watching many files

When processing a large number of files (e.g. reading or watching directories with thousands of files), Node.js throws: arduino Copy code Error: EMFILE: too many open files Even though .readFile() or .watch() is used, the process crashes. How can I reliably handle file I/O without hitting this limit?

This error occurs when the process tries to open more file descriptors than the OS limit allows (e.g. macOS default ~8192). Node’s asynchronous I/O opens many files simultaneously and may exhaust the available handles ([turn0search0]turn0search2turn0search10). Common causes: • Using fs.readFile() or readFileSync() in tight loops over many files. • Watching large directories via fs.watch() or similar, especially with symlink cycles you might not control ([turn0search2]). Fixes: • Use graceful-fs to queue file operations gracefully: js Copy code const fs = require('graceful-fs'); • Limit concurrency using queue utilities like async.eachLimit() or manual pooling: js Copy code async.eachLimit(files, 5, async (file) => { /* read & process */ }); • Explicitly close file handles when using fs.promises.open() inside try…finally blocks ([turn0search10]). • On macOS/React Native, consider installing watchman to offload file watching ([turn0search6]turn0search11). • As a last resort, increase OS limits via ulimit -n or update /etc/security/limits.conf, especially in dev environments with heavy watchers ([turn0search5].