3 files changed, 30 insertions, 4 deletions
diff --git a/js/deno.ts b/js/deno.ts
index 21c93c5d3..869314d2c 100644
--- a/js/deno.ts
+++ b/js/deno.ts
@@ -4,7 +4,17 @@
 /// <amd-module name="deno"/>
 export { env, exit } from "./os";
 export { chdir, cwd } from "./dir";
-export { File, open, stdin, stdout, stderr, read, write, close } from "./files";
+export {
+  File,
+  open,
+  stdin,
+  stdout,
+  stderr,
+  read,
+  write,
+  close,
+  OpenMode
+} from "./files";
 export {
   copy,
   toAsyncIterator,
diff --git a/js/files.ts b/js/files.ts
index 4392eadf7..e23d19cfe 100644
--- a/js/files.ts
+++ b/js/files.ts
@@ -29,7 +29,7 @@ export const stdout = new File(1);
 /** An instance of `File` for stderr. */
 export const stderr = new File(2);
 
-type OpenMode =
+export type OpenMode =
   /** Read-only. Default. Starts at beginning of file. */
   | "r"
   /** Read-write. Start at beginning of file. */
diff --git a/js/files_test.ts b/js/files_test.ts
index d46a46906..03ad7a7cd 100644
--- a/js/files_test.ts
+++ b/js/files_test.ts
@@ -30,10 +30,26 @@ test(async function filesToAsyncIterator() {
   assertEqual(totalSize, 12);
 });
 
+testPerm({ write: false }, async function writePermFailure() {
+  const filename = "tests/hello.txt";
+  const writeModes: deno.OpenMode[] = ["r+", "w", "w+", "a", "a+", "x", "x+"];
+  for (const mode of writeModes) {
+    let err;
+    try {
+      await deno.open(filename, mode);
+    } catch (e) {
+      err = e;
+    }
+    assert(!!err);
+    assertEqual(err.kind, deno.ErrorKind.PermissionDenied);
+    assertEqual(err.name, "PermissionDenied");
+  }
+});
+
 testPerm({ write: true }, async function createFile() {
   const tempDir = await deno.makeTempDir();
   const filename = tempDir + "/test.txt";
-  let f = await deno.open(filename, "w");
+  const f = await deno.open(filename, "w");
   let fileInfo = deno.statSync(filename);
   assert(fileInfo.isFile());
   assert(fileInfo.len === 0);
@@ -88,7 +104,7 @@ testPerm({ write: true }, async function openModeWriteRead() {
   const filename = tempDir + "hello.txt";
   const data = encoder.encode("Hello world!\n");
 
-  let file = await deno.open(filename, "w+");
+  const file = await deno.open(filename, "w+");
   // assert file was created
   let fileInfo = deno.statSync(filename);
   assert(fileInfo.isFile());