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What is the difference between fs.readFile() and fs.createReadStream() for reading a file in Node.js? What is the difference between an absolute path and a relative path in Node.js, and how does __dirname help resolve paths reliably? What is the difference between fs.unlink() and fs.rmdir() (or the newer fs.rm()) in Node.js? How would you safely check if a file exists in Node.js before attempting to read it, avoiding a race condition? What is the difference between fs.appendFile() and opening a file with the 'a' flag and writing to it manually? What is the difference between fs.stat() and fs.lstat(), and when does the distinction matter? How would you copy a large file efficiently in Node.js, and what's the difference between fs.copyFile() and manually piping streams? What is the purpose of the 'flag' option in fs.writeFile(), and what's the difference between 'w', 'a', and 'wx' flags? How would you implement a file-watching feature in Node.js using fs.watch(), and what are its known cross-platform limitations? How would you implement atomic file writes in Node.js to avoid leaving a file in a corrupted, half-written state if the process crashes mid-write?
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How would you recursively read all files within a directory tree in Node.js?

Intermediate

Answer

fs.readdir() with the 'recursive' option (Node 20+) returns every file and subdirectory path within a directory tree in one call, or for finer control (like filtering or processing files as they're discovered rather than all at once), you can manually walk the tree, calling fs.readdir() on each directory and recursing into any subdirectories found.
const fs = require('node:fs/promises');

const files = await fs.readdir('./project', { recursive: true, withFileTypes: true });
const jsFiles = files.filter(f => f.isFile() && f.name.endsWith('.js'));
Real-world example A code-linting tool recursively scans an entire project directory for all .js files using fs.readdir with the recursive option, avoiding the need to manually implement tree-walking logic that used to require a third-party package like glob.

Common follow-ups: How does the recursive option's behavior differ across Node.js versions where it wasn't yet available?;What's the performance consideration of reading an entire deep directory tree into memory at once versus processing it incrementally?

CLI Tools & Scripting with Node.js;Path & OS Modules
All 15 File System & File Processing questions