Add-ons using the techniques described in this document are considered a legacy technology in Firefox. Don't use these techniques to develop new add-ons. Use WebExtensions instead. If you maintain an add-on which uses the techniques described here, consider migrating it to use WebExtensions.
From Firefox 53 onwards, no new legacy add-ons will be accepted on addons.mozilla.org (AMO).
From Firefox 57 onwards, WebExtensions will be the only supported extension type, and Firefox will not load other types.
Even before Firefox 57, changes coming up in the Firefox platform will break many legacy extensions. These changes include multiprocess Firefox (e10s), sandboxing, and multiple content processes. Legacy extensions that are affected by these changes should migrate to WebExtensions if they can. See the "Compatibility Milestones" document for more.
A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.
Experimental
Provides access to the local filesystem.
Usage
Paths
Path specifications in this API are platform-specific. This means that on Windows paths are specified using the backslash path separator (\), and on Unix-like systems like Linux and OS X paths are specified using the forward slash path separator (/).
If your add-on uses literal Windows-style path specifications with this API, your add-on likely won't work when users run it on Unix-like systems. Likewise, if your add-on uses literal Unix-style path specifications, it won't work for users on Windows.
To ensure your add-on works for everyone, generate paths using the join function. Unfortunately this API does not currently provide a way to obtain an absolute base path which you could then use with join. For now, you need to require("chrome") and use the XPCOM directory service as described in this article about File I/O.
Note that if you do decide to hardcode Windows-style paths, be sure to escape backslashes in strings. For example, to specify the file at C:\Users\Myk, you need to use the string "C:\\Users\\Myk", not "C:\Users\Myk". Read more about escaping characters in strings.
Globals
Functions
basename(path)
The path parameter must be an absolute path, relative paths will cause an error.
Use the fs/path module for relative path support.
Returns the last component of the given path. For example, basename("/foo/bar/baz") returns "baz". If the path has no components, the empty string is returned.
Parameters
path : string
The path of a file.
Returns
string : The last component of the given path.
dirname(path)
Returns the path of the directory containing the given file. If the file is at the top of the volume, the empty string is returned.
Parameters
path : string
The path of a file.
Returns
string : The path of the directory containing the file.
exists(path)
Returns true if a file exists at the given path and false otherwise.
Parameters
path : string
The path of a file.
Returns
boolean : True if the file exists and false otherwise.
join(...)
Takes a variable number of strings, joins them on the file system's path separator, and returns the result.
Parameters
... : strings
A variable number of strings to join. The first string must be an absolute path.
Returns
string : A single string formed by joining the strings on the file system's path separator.
list(path)
Returns an array of file names in the given directory.
Parameters
path : string
The path of the directory.
Returns
array : An array of file names. Each is a basename, not a full path.
mkpath(path)
Makes a new directory named by the given path. Any subdirectories that do not exist are also created. mkpath can be called multiple times on the same path.
Parameters
path : string
The path to create.
open(path, mode)
Returns a stream providing access to the contents of a file.
Parameters
path : string
The path of the file to open.
mode : string
An optional string, each character of which describes a characteristic of the returned stream.
- If the string contains
"r", the file is opened in read-only mode. "w"opens the file in write-only mode."b"opens the file in binary mode. If"b"is not present, the file is opened in text mode, and its contents are assumed to be UTF-8.
If mode is not given, "r" is assumed, and the file is opened in read-only text mode.
Apart from these options, this API always passes the following options: CREATE_FILE, TRUNCATE (see https://dxr.mozilla.org/mozilla-central/source/nsprpub/pr/include/prio.h#550). This means that:
- if the file does not exist it is created
- if the file exists, its length is truncated to zero
- it is not possible to open the file in append mode.
Returns
stream : If the file is opened in text read-only mode, a TextReader is returned, and if text write-only mode, a TextWriter is returned. See text-streams for information on these text stream objects. If the file is opened in binary read-only mode, a ByteReader is returned, and if binary write-only mode, a ByteWriter is returned. See byte-streams for more information on these byte stream objects. Opened files should always be closed after use by calling close on the returned stream.
read(path, mode)
Opens a file and returns a string containing its entire contents.
Parameters
path : string
The path of the file to read.
mode : string
An optional string, each character of which describes a characteristic of the returned stream. If the string contains "b", the contents will be returned in binary mode. If "b" is not present or mode is not given, the file contents will be returned in text mode.
Returns
string : A string containing the file's entire contents.
remove(path)
Removes a file from the file system. To remove directories, use rmdir.
Parameters
path : string
The path of the file to remove.
rmdir(path)
Removes a directory from the file system. If the directory is not empty, an exception is thrown.
Parameters
path : string
The path of the directory to remove.
isFile(path)
Returns true only if this path specifies a file.
const fileIO = require("sdk/io/file");
let path = "/Users/Work/";
let list = fileIO.list(path);
for (i = 0; i < list.length; i++) {
let item = fileIO.join(path, list[i]);
if (fileIO.isFile(item)) {
console.log(item + " is a file");
}
else {
console.log(item + " is a directory");
}
}
Parameters
path : string
The path of the object.