FileSystemHandle: requestPermission() 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.

TypeError

Thrown if no parameter is specified or the mode is not that of 'read' or 'readwrite'

SecurityError DOMException

Thrown in one of the following cases:

• The method was called in a context that's not same-origin as the top-level context (i.e. a cross-origin iframe).
• There was no transient user activation such as a button press. This includes when the handle is in a non-Window context which cannot consume user activation, such as a worker.

Transient user activation is required. The user has to interact with the page or a UI element in order for this feature to work.

The following asynchronous function requests permissions if they have not been granted.

// 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