FileSystemFileHandle
Baseline Widely available *
This feature is well established and works across many devices and browser versions. It’s been available across browsers since March 2023.
* Some parts of this feature may have varying levels of support.
Secure context: This feature is available only insecure contexts (HTTPS), in some or allsupporting browsers.
Note: This feature is available inWeb Workers.
TheFileSystemFileHandle interface of theFile System API represents a handle to a file system entry. The interface is accessed through thewindow.showOpenFilePicker() method.
Note that read and write operations depend on file-access permissions that do not persist after a page refresh if no other tabs for that origin remain open. ThequeryPermission method of theFileSystemHandle interface can be used to verify permission state before accessing a file.
Instance properties
Inherits properties from its parent,FileSystemHandle.
Instance methods
Inherits methods from its parent,FileSystemHandle.
getFile()Returns a
Promisewhich resolves to aFileobjectrepresenting the state on disk of the entry represented by the handle.createSyncAccessHandle()Returns a
Promisewhich resolves to aFileSystemSyncAccessHandleobjectthat can be used to synchronously read from and write to a file. The synchronous nature of this method brings performance advantages,but it is only usable inside dedicatedWeb Workers.createWritable()Returns a
Promisewhich resolves to a newly createdFileSystemWritableFileStreamobject that can be used to write to a file.
Examples
Reading a File
The following asynchronous function presents a file picker and once a file is chosen, uses thegetFile() method to retrieve the contents.
async function getTheFile() { const pickerOpts = { types: [ { description: "Images", accept: { "image/*": [".png", ".gif", ".jpeg", ".jpg"], }, }, ], excludeAcceptAllOption: true, multiple: false, }; // open file picker const [fileHandle] = await window.showOpenFilePicker(pickerOpts); // get file contents const fileData = await fileHandle.getFile(); return fileData;}Writing a File
The following asynchronous function writes the given contents to the file handle, and thus to disk.
async function writeFile(fileHandle, contents) { // Create a FileSystemWritableFileStream to write to. const writable = await fileHandle.createWritable(); // Write the contents of the file to the stream. await writable.write(contents); // Close the file and write the contents to disk. await writable.close();}Synchronously reading and writing a file
The following asynchronous event handler function is contained inside a Web Worker. On receiving a message from the main thread it:
- Creates a synchronous file access handle.
- Gets the size of the file and creates an
ArrayBufferto contain it. - Reads the file contents into the buffer.
- Encodes the message and writes it to the end of the file.
- Persists the changes to disk and closes the access handle.
onmessage = async (e) => { // Retrieve message sent to work from main script const message = e.data; // Get handle to draft file const root = await navigator.storage.getDirectory(); const draftHandle = await root.getFileHandle("draft.txt", { create: true }); // Get sync access handle const accessHandle = await draftHandle.createSyncAccessHandle(); // Get size of the file. const fileSize = accessHandle.getSize(); // Read file content to a buffer. const buffer = new DataView(new ArrayBuffer(fileSize)); const readBuffer = accessHandle.read(buffer, { at: 0 }); // Write the message to the end of the file. const encoder = new TextEncoder(); const encodedMessage = encoder.encode(message); const writeBuffer = accessHandle.write(encodedMessage, { at: readBuffer }); // Persist changes to disk. accessHandle.flush(); // Always close FileSystemSyncAccessHandle if done. accessHandle.close();};Note:In earlier versions of the spec,close(),flush(),getSize(), andtruncate() were wrongly specified as asynchronous methods, and older versions of some browsers implement them in this way. However, all current browsers that support these methods implement them as synchronous methods.
Specifications
| Specification |
|---|
| File System # api-filesystemfilehandle |