FileSystemHandle: queryPermission() method

descriptor Optional

An object which specifies the permission mode to query for. Options are as follows:

'mode' Optional

Can be either 'read' or 'readwrite'.

A Promise that resolves with PermissionStatus.state which is one of 'granted', 'denied' or 'prompt'. It may also reject with one of the exceptions below.

If this resolves with "prompt", the website will have to call requestPermission() before any operations on the handle can be done. If this resolves with "denied" any operations will reject. Usually handles returned by the local file system handle factories will initially resolves with "granted" for their read permission state. However, other than through the user revoking permission, a handle retrieved from IndexedDB is also likely to resolves with "prompt".

TypeError

Thrown if mode is specified with a value other than 'read' or 'readwrite'

The following asynchronous function returns true if user has granted read or readwrite permissions to the file handle. Permission is requested if not.

// fileHandle is a FileSystemFileHandle
// withWrite is a boolean set to true if write

async function verifyPermission(fileHandle, withWrite) {
  const opts = {};
  if (withWrite) {
    opts.mode = "readwrite";
  }

  // Check if we already have permission, if so, return true.
  if ((await fileHandle.queryPermission(opts)) === "granted") {
    return true;
  }

  // Request permission to the file, if the user grants permission, return true.
  if ((await fileHandle.requestPermission(opts)) === "granted") {
    return true;
  }

  // The user did not grant permission, return false.
  return false;
}

• File System API
• The File System Access API: simplifying access to local files