File System, Processes and Signals

Key points

1. 1

   Sync fs calls block the whole event loop. Use them at startup or in CLIs, and use fs/promises or streams inside servers; stream large files instead of readFile.

2. 2

   Relative fs paths resolve against process.cwd(), not the module. Build paths from __dirname (CommonJS) or import.meta.dirname (ESM, Node.js 20.11+). path.join concatenates; path.resolve restarts at the last absolute segment.

3. 3

   Avoid check-then-act races: open with the wx flag instead of existsSync + write, and write atomically with a temp file in the same folder plus rename (renaming across filesystems fails with EXDEV).

4. 4

   Prefer process.exitCode over process.exit(): exit() abandons timers and pending stdout writes. The exit event only runs synchronous code; beforeExit can schedule more work.

5. 5

   Signals: SIGINT and SIGTERM exit with 128 + signal (130, 143) unless you add a listener, which removes the default. As PID 1 in a container, Node.js ignores SIGTERM unless it handles it; use the exec form of CMD and --init.

6. 6

   child_process: exec uses a shell and buffers up to maxBuffer (1 MiB); execFile and spawn take argument arrays without a shell; fork adds an IPC channel. Consume piped stdout, and use detached + unref() for background children.

7. 7

   Built-ins replace common packages: --env-file (environment values win, later files override), util.parseArgs (strict by default), --watch, node:sqlite, and the opt-in --permission model.

Read the source

• File system
• Process
• Child process