2 files changed, 22 insertions, 4 deletions
diff --git a/cli/js/web/url.ts b/cli/js/web/url.ts
index 76aa21919..60690d46a 100644
--- a/cli/js/web/url.ts
+++ b/cli/js/web/url.ts
@@ -62,12 +62,15 @@ function parse(url: string, isBase = true): URLParts | undefined {
     parts.password = "";
     [parts.hostname, restUrl] = takePattern(restUrl, /^[/\\]{2}([^/\\?#]*)/);
     parts.port = "";
+    if (build.os == "windows" && parts.hostname == "") {
+      // UNC paths. e.g. "\\\\localhost\\foo\\bar" on Windows should be
+      // representable as `new URL("file:////localhost/foo/bar")` which is
+      // equivalent to: `new URL("file://localhost/foo/bar")`.
+      [parts.hostname, restUrl] = takePattern(restUrl, /^[/\\]{2,}([^/\\?#]*)/);
+    }
   } else if (specialSchemes.includes(parts.protocol)) {
     let restAuthority;
-    [restAuthority, restUrl] = takePattern(
-      restUrl,
-      /^[/\\]{2}[/\\]*([^/\\?#]+)/
-    );
+    [restAuthority, restUrl] = takePattern(restUrl, /^[/\\]{2,}([^/\\?#]+)/);
     if (isBase && restAuthority == "") {
       return undefined;
     }
diff --git a/cli/tests/unit/url_test.ts b/cli/tests/unit/url_test.ts
index b4c31ea6d..d22787f1c 100644
--- a/cli/tests/unit/url_test.ts
+++ b/cli/tests/unit/url_test.ts
@@ -191,6 +191,21 @@ unitTest(function urlDriveLetter() {
   assertEquals(new URL("http://example.com/C:").href, "http://example.com/C:");
 });
 
+unitTest(function urlUncHostname() {
+  assertEquals(
+    new URL("file:////").href,
+    Deno.build.os == "windows" ? "file:///" : "file:////"
+  );
+  assertEquals(
+    new URL("file:////server").href,
+    Deno.build.os == "windows" ? "file://server/" : "file:////server"
+  );
+  assertEquals(
+    new URL("file:////server/file").href,
+    Deno.build.os == "windows" ? "file://server/file" : "file:////server/file"
+  );
+});
+
 unitTest(function urlHostnameUpperCase() {
   assertEquals(new URL("https://EXAMPLE.COM").href, "https://example.com/");
 });