The fs Module

The fs (file system) module lets you work with files: read, write, append, and delete. It is built into Node.js, so no installation is needed.

Reading a file (async)

The async version takes a callback and does not block the program.

const fs = require("fs");

fs.readFile("note.txt", "utf8", (err, data) => {
  if (err) {
    return console.error(err);
  }
  console.log(data);
});

Writing a file (async)

const fs = require("fs");

fs.writeFile("note.txt", "Hello file!", (err) => {
  if (err) throw err;
  console.log("File saved");
});

Synchronous versions

The sync versions block until done. They are simpler but stop everything while running.

const fs = require("fs");

const data = fs.readFileSync("note.txt", "utf8");
console.log(data);

fs.writeFileSync("note.txt", "New content");

Sync vs async

• Use async in servers so other work continues.
• Use sync only for simple scripts or startup code.

Summary

The fs module is your gateway to files. Prefer the async methods for anything that handles many requests.