DirectoryReaderSync

Non-standard: This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

The DirectoryReaderSync interface lets you read the entries in a directory.

Warning: This interface is deprecated and is no more on the standard track. Do not use it anymore. Use the File and Directory Entries API instead.

Basic concepts

Before you call the only method in this interface, readEntries(), create the DirectoryEntrySync object. But DirectoryEntrySync (as well as FileEntrySync) is not a data type that you can pass between a calling app and Web Worker thread. It's not a big deal, because you don't really need to have the main app and the worker thread see the same JavaScript object; you just need them to access the same files. You can do that by passing a list of filesystem: URLs—which are just strings—instead of a list of entries. You can also use the filesystem: URL to look up the entry with resolveLocalFileSystemURL(). That gets you back to a DirectoryEntrySync (as well as FileEntrySync) object.

Example

In the following code snippet from HTML5Rocks (web.dev), we create Web Workers and pass data from it to the main app.

js
// Taking care of the browser-specific prefixes.
window.resolveLocalFileSystemURL =
  window.resolveLocalFileSystemURL || window.webkitResolveLocalFileSystemURL;

// Create web workers
const worker = new Worker("worker.js");
worker.onmessage = (e) => {
  const urls = e.data.entries;
  urls.forEach((url) => {
    window.resolveLocalFileSystemURL(url, (fileEntry) => {
      // Print out file's name.
      console.log(fileEntry.name);
    });
  });
};

worker.postMessage({ cmd: "list" });

The following is worker.js code that gets the contents of the directory.

js
// worker.js

// Taking care of the browser-specific prefixes.
self.requestFileSystemSync =
  self.webkitRequestFileSystemSync || self.requestFileSystemSync;

// Global for holding the list of entry file system URLs.
const paths = [];

function getAllEntries(dirReader) {
  const entries = dirReader.readEntries();

  for (const entry of entries) {
    // Stash this entry's filesystem in URL
    paths.push(entry.toURL());

    // If this is a directory, traverse.
    if (entry.isDirectory) {
      getAllEntries(entry.createReader());
    }
  }
}

// Forward the error to main app.
function onError(e) {
  postMessage(`ERROR: ${e.toString()}`);
}

self.onmessage = (e) => {
  const cmd = e.data.cmd;

  // Ignore everything else except our 'list' command.
  if (!cmd || cmd !== "list") {
    return;
  }

  try {
    const fs = requestFileSystemSync(TEMPORARY, 1024 * 1024 /*1MB*/);

    getAllEntries(fs.root.createReader());

    self.postMessage({ entries: paths });
  } catch (e) {
    onError(e);
  }
};

Method

readEntries()

Returns a list of entries from a specific directory. Call this method until an empty array is returned.

Syntax

js
readEntries()
Parameters

None.

Return value

Array containing FileEntrySync and DirectoryEntrySync.

Exceptions

This method can raise a DOMException with the following codes:

Exception Description
NOT_FOUND_ERR The directory does not exist.
INVALID_STATE_ERR The directory has been modified since the first call to readEntries was processed.
SECURITY_ERR The browser determined that it was not safe to look up the metadata.

Specifications

This feature is not part of any specification anymore. It is no longer on track to become a standard.

Browser compatibility

BCD tables only load in the browser

See also