fs module

File System is an essential built-in module of Node that contains utility methods for working with files and directories.

Every method associated with fs has a blocking and asynchronous implementation. The former obviously blocks the event queue, the latter does not.

The synchronous methods are useful to have in some contexts but in general and with real-world applications, you should be using the async implementation so as to accord with the single-threaded event-driven architecture of Node.

Common I/0 methods

Read directory

Return a string array of all files in the current directory.

fs.readdir("./", function (err, files) {
  if (err) {
    console.error(err);
  } else {
    console.log(files);
  }
});

Read from file

fs.readFile("./lorem.md", "UTF-8", function (err, fileContents) {
  console.log(fileContents);
});

Write to file

let md = `A new file`;

fs.writeFile("testFile.md", md.trim(), function () {
  console.log("File was created");
});

Appending to file

fs.appendFile("testFile.md", "new content");

Create directory

if (!fs.existsSync("directory_name")) {
  fs.mkdir("directory_name", function (err) {
    if (err) {
      console.err(err);
    }
  });
} else {
  console.warn("Directory already exists");
}

Rename and remove files

fs.rename("./filename.js", "./newname.js", function () {
  console.log("file renamed");
});
// Remove file
fs.unlink("./file-to-delete", function (err) {
  if (err) {
    console.error(err);
  }
});

Rename and remove directories

// Best to use synchronous method here
fs.rmSync("/dir", { recursive: true, force: true });

Streams

See Handling streams with fs

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