3 files changed, 41 insertions, 0 deletions
diff --git a/js/deno.ts b/js/deno.ts
index 21766401b..d121b3183 100644
--- a/js/deno.ts
+++ b/js/deno.ts
@@ -6,6 +6,7 @@ export {
   exit,
   FileInfo,
   makeTempDirSync,
+  mkdirSync,
   readFileSync,
   statSync,
   lStatSync,
diff --git a/js/os.ts b/js/os.ts
index e669aea9d..cca121874 100644
--- a/js/os.ts
+++ b/js/os.ts
@@ -104,6 +104,25 @@ export function makeTempDirSync({
   return path!;
 }
 
+// mkdir creates a new directory with the specified name
+// and permission bits  (before umask).
+export function mkdirSync(path: string, mode = 0o777): void {
+  /* Ideally we could write:
+  const res = send({
+    command: fbs.Command.MKDIR_SYNC,
+    mkdirSyncPath: path,
+    mkdirSyncMode: mode,
+  });
+  */
+  const builder = new flatbuffers.Builder();
+  const path_ = builder.createString(path);
+  fbs.MkdirSync.startMkdirSync(builder);
+  fbs.MkdirSync.addPath(builder, path_);
+  fbs.MkdirSync.addMode(builder, mode);
+  const msg = fbs.MkdirSync.endMkdirSync(builder);
+  send(builder, fbs.Any.MkdirSync, msg);
+}
+
 export function readFileSync(filename: string): Uint8Array {
   /* Ideally we could write
   const res = send({
diff --git a/js/os_test.ts b/js/os_test.ts
index cd5ede221..8142956eb 100644
--- a/js/os_test.ts
+++ b/js/os_test.ts
@@ -183,3 +183,24 @@ test(function makeTempDirSyncPerm() {
   assert(err);
   assertEqual(err.name, "deno.PermissionDenied");
 });
+
+testPerm({ write: true }, function mkdirSync() {
+  const path = deno.makeTempDirSync() + "/dir/subdir";
+  deno.mkdirSync(path);
+  const pathInfo = deno.statSync(path);
+  assert(pathInfo.isDirectory());
+});
+
+testPerm({ write: false }, function mkdDirSyncPerm() {
+  let err;
+  try {
+    const path = "/baddir";
+    deno.mkdirSync(path);
+  } catch (err_) {
+    err = err_;
+  }
+  // TODO assert(err instanceof deno.PermissionDenied).
+  assert(err);
+  assertEqual(err.name, "deno.PermissionDenied");
+});
+