File System Module

File System Module

The fs module lets you interact with the file system. You can read, write, delete, and modify files and directories.

Reading Files

const fs = require("fs").promises;

// Async (recommended)
async function readFile() {
  try {
    const data = await fs.readFile("data.txt", "utf-8");
    console.log(data);
  } catch (err) {
    console.error(err);
  }
}

// Synchronous (blocks event loop)
const data = fs.readFileSync("data.txt", "utf-8");

Writing Files

// Create or overwrite
await fs.writeFile("output.txt", "Hello, World!");

// Append to file
await fs.appendFile("output.txt", "\nNew line");

// Write JSON
await fs.writeFile("data.json", JSON.stringify(data, null, 2));

Working with Directories

// Create directory
await fs.mkdir("new-folder", { recursive: true });

// Read directory contents
const files = await fs.readdir("./");

// Check if file/directory exists
try {
  await fs.access("file.txt");
  console.log("File exists");
} catch {
  console.log("File does not exist");
}

// Delete
await fs.unlink("file.txt");
await fs.rm("folder", { recursive: true });

File Streams

For large files, use streams instead of reading everything into memory:

const fs = require("fs");

// Read stream
const readStream = fs.createReadStream("large-file.txt");
readStream.on("data", (chunk) => {
  console.log(`Received ${chunk.length} bytes`);
});

// Write stream
const writeStream = fs.createWriteStream("output.txt");
writeStream.write("Hello ");
writeStream.write("World!");
writeStream.end();