Skip to content
Expose the file system on the user’s device, so Web apps can interoperate with the user’s native applications.
Branch: master
Clone or download
mkruisselbrink Add opaque origin checks to API entry points. (#105)
* Add opaque origin checks to API entry points.

Also adds a check for first-party-context only to the
chooseFileSystemEntries API.

Fixes #77

* Slightly simplify first-party context check
Latest commit 533b736 Nov 18, 2019

Native File System API

View proposals in the EXPLAINER and the (very early draft) spec.


Today, if a web site wants to create experiences involving local files (document editor, image compressor, etc.) they are at a disadvantage to native apps. A web site must ask the user to reopen a file every time they want to edit it. After opening, the site can only save changes by re downloading the file to the Downloads folder. A native app, by comparison, can maintain a most recently used list, auto save, and save files anywhere the user wants.

Use cases

  • Open local file to read
  • Open local file to edit and then save
  • Open local file to edit with auto save
  • Create and save a new file
  • Delete an existing file
  • Read meta data about files


  • FileSaver.js polyfills saveAs() from the W3C File API, but files open in a new window instead of downloading on Safari 6.1+ and iOS.
  • In Edge, Firefox, and Chrome developers can:
    • Create a fake anchor element (var a = document.createElement('a'))
    • Set download to the desired filename ( = 'file.txt')
    • Set href to a data URI or Blob URL (a.href = URL.createObjectURL(blob))
    • Fake a click on the anchor element (
    • Clean up if necessary (URL.revokeObjectURL(a.href))
  • Setting window.location to 'data:application/octet-stream' + data_stream
  • Hidden Flash controls to display a “save as” dialog

These methods are clunky and only support “save as” (and depending on the UA may automatically appear in Downloads without prompting the user for location). They do not support most recently used lists, auto save, save, or deleting a file.

You can’t perform that action at this time.