Guides File System

Watch a directory for changes

Bun implements the node:fs module, including the fs.watch function for listening for file system changes.

The following code listens for changes to files in the current directory. By default the watch is shallow: changes to files in subdirectories are not detected.

import { watch } from "fs";

const watcher = watch(import.meta.dir, (event, filename) => {
  console.log(`Detected ${event} in ${filename}`);
});

To listen for changes in subdirectories, pass the recursive: true option to fs.watch.

import { watch } from "fs";

const watcher = watch(import.meta.dir, { recursive: true }, (event, relativePath) => {
  console.log(`Detected ${event} in ${relativePath}`);
});

With the node:fs/promises module, you can listen for changes with for await...of instead of a callback.

import { watch } from "fs/promises";

const watcher = watch(import.meta.dir);
for await (const event of watcher) {
  console.log(`Detected ${event.eventType} in ${event.filename}`);
}

To stop listening for changes, call watcher.close(). It's common to do this when the process receives a SIGINT signal, such as when the user presses Ctrl-C.

import { watch } from "fs";

const watcher = watch(import.meta.dir, (event, filename) => {
  console.log(`Detected ${event} in ${filename}`);
});

process.on("SIGINT", () => {
  // close watcher when Ctrl-C is pressed
  console.log("Closing watcher...");
  watcher.close();

  process.exit(0);
});

Refer to API > Binary data > Typed arrays for more information on working with Uint8Array and other binary data formats in Bun.

Read to Uint8Array

Append to file

Watch a directory for changes

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