doc: clarify return type of fs.mkdtemp*

doc/api/fs.md

@@ -1652,8 +1652,10 @@ changes:
 * `prefix` {string|Buffer|URL}
 * `options` {string|Object}
   * `encoding` {string} **Default:** `'utf8'`
-* Returns: {Promise}  Fulfills with a string containing the file system path
-  of the newly created temporary directory.
+* Returns: {Promise} Fulfills with the created directory path.
+  If `encoding` is `'buffer'`, then the resulting directory
+  path is returned as a {Buffer}. Otherwise, the path is returned as a
+  {string} using the specified encoding.
 
 Creates a unique temporary directory. A unique directory name is generated by
 appending six random characters to the end of the provided `prefix`. Due to
@@ -1692,14 +1694,15 @@ added: v24.4.0
 * `options` {string|Object}
   * `encoding` {string} **Default:** `'utf8'`
 * Returns: {Promise} Fulfills with a Promise for an async-disposable Object:
-  * `path` {string} The path of the created directory.
+  * `path` {string|Buffer} The path of the created directory.
   * `remove` {AsyncFunction} A function which removes the created directory.
   * `[Symbol.asyncDispose]` {AsyncFunction} The same as `remove`.
 
 The resulting Promise holds an async-disposable object whose `path` property
-holds the created directory path. When the object is disposed, the directory
-and its contents will be removed asynchronously if it still exists. If the
-directory cannot be deleted, disposal will throw an error. The object has an
+holds the created directory path. If `encoding` is `'buffer'`, the `path` will
+also be a {Buffer}, otherwise a {string}. When the object is disposed, the
+directory and its contents will be removed asynchronously if it still exists. If
+the directory cannot be deleted, disposal will throw an error. The object has an
 async `remove()` method which will perform the same task.
 
 Both this function and the disposal function on the resulting object are
@@ -4008,7 +4011,7 @@ changes:
   * `encoding` {string} **Default:** `'utf8'`
 * `callback` {Function}
   * `err` {Error}
-  * `directory` {string}
+  * `directory` {string|Buffer}
 
 Creates a unique temporary directory.
 
@@ -4018,12 +4021,14 @@ inconsistencies, avoid trailing `X` characters in `prefix`. Some platforms,
 notably the BSDs, can return more than six random characters, and replace
 trailing `X` characters in `prefix` with random characters.
 
-The created directory path is passed as a string to the callback's second
-parameter.
-
 The optional `options` argument can be a string specifying an encoding, or an
 object with an `encoding` property specifying the character encoding to use.
 
+The created directory path is passed to the callback's second parameter. If
+`encoding` is `'buffer'`, then the resulting directory path is passed as a
+{Buffer}. Otherwise, the path is passed as a {string} using the specified
+encoding.
+
 ```mjs
 import { mkdtemp } from 'node:fs';
 import { join } from 'node:path';
@@ -6500,9 +6505,11 @@ changes:
 * `prefix` {string|Buffer|URL}
 * `options` {string|Object}
   * `encoding` {string} **Default:** `'utf8'`
-* Returns: {string}
+* Returns: {string|Buffer}
 
-Returns the created directory path.
+Returns the created directory path. If `encoding` is `'buffer'`, then the
+resulting directory path is returned as a {Buffer}. Otherwise, the path
+is returned as a {string} using the specified encoding.
 
 For detailed information, see the documentation of the asynchronous version of
 this API: [`fs.mkdtemp()`][].
@@ -6520,15 +6527,15 @@ added: v24.4.0
 * `options` {string|Object}
   * `encoding` {string} **Default:** `'utf8'`
 * Returns: {Object} A disposable object:
-  * `path` {string} The path of the created directory.
+  * `path` {string|Buffer} The path of the created directory.
   * `remove` {Function} A function which removes the created directory.
   * `[Symbol.dispose]` {Function} The same as `remove`.
 
 Returns a disposable object whose `path` property holds the created directory
-path. When the object is disposed, the directory and its contents will be
-removed if it still exists. If the directory cannot be deleted, disposal will
-throw an error. The object has a `remove()` method which will perform the same
-task.
+path. If `encoding` is `'buffer'`, the `path` will be a {Buffer}. When the
+object is disposed, the directory and its contents will be removed if it still
+exists. If the directory cannot be deleted, disposal will throw an error. The
+object has a `remove()` method which will perform the same task.
 
 See the [MDN documentation on `using` statements][`using`] for more information about
 explicit resource management.