vfs: return string from mountPointURL

Author: mcollina

doc/api/vfs.md

@@ -208,11 +208,11 @@ mounted.
 added: REPLACEME
 -->
 
-* {URL | null}
+* {string | null}
 
-The current mount point as a `file:` {URL}, or `null` when the VFS is
-not mounted. A fresh `URL` object is returned on each access, so
-mutating the result does not affect the instance.
+The current mount point as a `file:` URL string (the [`vfs.mountPoint`][]
+path converted with [`url.pathToFileURL()`][]), or `null` when the VFS
+is not mounted.
 
 This is a convenience for addressing mounted files with URL-based
 APIs such as dynamic `import()`:
@@ -544,8 +544,10 @@ fields use synthetic but stable values:
 [`node:fs`]: fs.md
 [`require()`]: modules.md#requireid
 [`require.resolve()`]: modules.md#requireresolverequest-options
+[`url.pathToFileURL()`]: url.md#urlpathtofileurlpath-options
 [`vfs.mount()`]: #vfsmount
 [`vfs.mountPointURL`]: #vfsmountpointurl
+[`vfs.mountPoint`]: #vfsmountpoint
 [`vfs.unmount()`]: #vfsunmount
 [loading from `node_modules` folders]: modules.md#loading-from-node_modules-folders
 [the global folders]: modules.md#loading-from-the-global-folders

lib/internal/vfs/file_system.js

@@ -129,14 +129,14 @@ class VirtualFileSystem {
   }
 
   /**
-   * Gets the mount point as a `file:` URL, or null if not mounted.
-   * A fresh URL object is returned on each access.
-   * @returns {URL|null}
+   * Gets the mount point as a `file:` URL string, or null if not
+   * mounted.
+   * @returns {string|null}
    */
   get mountPointURL() {
     if (this[kMountPoint] === null) return null;
     const { pathToFileURL } = require('internal/url');
-    return pathToFileURL(this[kMountPoint]);
+    return pathToFileURL(this[kMountPoint]).href;
   }
 
   /**

test/parallel/test-vfs-mount-point-url.js

@@ -13,36 +13,21 @@ const vfs = require('node:vfs');
   assert.strictEqual(myVfs.mountPointURL, null);
 }
 
-// Test: file: URL of the mount point while mounted, null again after
-// unmounting.
+// Test: file: URL string of the mount point while mounted, null again
+// after unmounting.
 {
   const myVfs = vfs.create();
   const mountPoint = myVfs.mount();
 
   const url = myVfs.mountPointURL;
-  assert.ok(url instanceof URL);
-  assert.strictEqual(url.protocol, 'file:');
-  assert.strictEqual(url.href, pathToFileURL(mountPoint).href);
+  assert.strictEqual(typeof url, 'string');
+  assert.ok(url.startsWith('file:'));
+  assert.strictEqual(url, pathToFileURL(mountPoint).href);
 
   myVfs.unmount();
   assert.strictEqual(myVfs.mountPointURL, null);
 }
 
-// Test: each access returns a fresh URL object, so callers mutating the
-// result cannot corrupt the instance state.
-{
-  const myVfs = vfs.create();
-  myVfs.mount();
-
-  const first = myVfs.mountPointURL;
-  first.pathname += '/tampered';
-  const second = myVfs.mountPointURL;
-  assert.notStrictEqual(first, second);
-  assert.strictEqual(second.href, pathToFileURL(myVfs.mountPoint).href);
-
-  myVfs.unmount();
-}
-
 // Test: the URL is usable to address files in the mounted VFS.
 {
   const myVfs = vfs.create();