Browser-NativeFS

This module allows you to easily use the Native File System API on supporting browsers, with a transparent fallback to the <input type="file"> and <a download> legacy methods. This library is a ponyfill.

Read more on the background of this module in my post Progressive Enhancement In the Age of Fugu APIs.

Live Demo

See the library in action: https://browser-nativefs.glitch.me/.

Origin Trial

⚠️ In order to use the Native File System API, you need to quickly request an origin trial token for your application and communicate it to the browser via a meta tag or an HTTP header.

Usage Example

The module feature-detects support for the Native File System API and only loads the actually relevant code.

// The imported methods will use the Native
// File System API or a fallback implementation.
import {
  fileOpen,
  directoryOpen,
  fileSave,
} from 'https://unpkg.com/browser-nativefs';

(async () => {
  // Open a file.
  const blob = await fileOpen({
    mimeTypes: ['image/*'],
  });

  // Open multiple files.
  const blobs = await fileOpen({
    mimeTypes: ['image/*'],
    multiple: true,
  });

  // Open all files in a directory,
  // recursively including subdirectories.
  const blobsInDirectory = await directoryOpen({
    recursive: true,
  });

  // Save a file.
  await fileSave(blob, {
    fileName: 'Untitled.png',
    extensions: ['png'],
  });
})();

API Documentation

Opening files:

// Options are optional.
const options = {
  // List of allowed MIME types, defaults to `*/*`.
  mimeTypes: ['image/*'],
  // List of allowed file extensions, defaults to `''`.
  extensions: ['png', 'jpg', 'jpeg', 'webp'],
  // Set to `true` for allowing multiple files, defaults to `false`.
  multiple: true,
  // Textual description for file dialog , defaults to `''`.
  description: 'Image files',
};

const blobs = await fileOpen(options);

Opening directories:

// Options are optional.
const options = {
  // Set to `true` to recursively open files in all subdirectories,
  // defaults to `false`.
  recursive: true,
};

const blobs = await directoryOpen(options);

The module also polyfills a webkitRelativePath property on returned files in a consistent way, regardless of the underlying implementation.

Saving files:

// Options are optional.
const options = {
  // Suggested file name to use, defaults to `''`.
  fileName: 'Untitled.txt',
  // Suggested file extensions, defaults to `''`.
  extensions: ['txt'],
};

// Optional file handle to save back to an existing file.
// This will only work with the Native File System API.
// Get a `FileHandle` from the `handle` property of the `Blob`
// you receive from `fileOpen()` (this is non-standard).
const handle = previouslyOpenedBlob.handle;

await fileSave(someBlob, options, handle);