feat(std/node): fs.writefile / fs.promises.writeFile (#5054)

10 files changed, 522 insertions, 121 deletions

diff --git a/std/node/_fs/_fs_appendFile.ts b/std/node/_fs/_fs_appendFile.ts
index b116589a0..c0f347dbf 100644
--- a/std/node/_fs/_fs_appendFile.ts
+++ b/std/node/_fs/_fs_appendFile.ts
@@ -1,5 +1,10 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-import { FileOptions, isFileOptions, CallbackWithError } from "./_fs_common.ts";
+import {
+  WriteFileOptions,
+  isFileOptions,
+  CallbackWithError,
+  getOpenOptions,
+} from "./_fs_common.ts";
 import { notImplemented } from "../_utils.ts";
 import { fromFileUrl } from "../path.ts";
 
@@ -10,13 +15,13 @@ import { fromFileUrl } from "../path.ts";
 export function appendFile(
   pathOrRid: string | number | URL,
   data: string,
-  optionsOrCallback: string | FileOptions | CallbackWithError,
+  optionsOrCallback: string | WriteFileOptions | CallbackWithError,
   callback?: CallbackWithError
 ): void {
   pathOrRid = pathOrRid instanceof URL ? fromFileUrl(pathOrRid) : pathOrRid;
   const callbackFn: CallbackWithError | undefined =
     optionsOrCallback instanceof Function ? optionsOrCallback : callback;
-  const options: string | FileOptions | undefined =
+  const options: string | WriteFileOptions | undefined =
     optionsOrCallback instanceof Function ? undefined : optionsOrCallback;
   if (!callbackFn) {
     throw new Error("No callback function supplied");
@@ -74,7 +79,7 @@ function closeRidIfNecessary(isPathString: boolean, rid: number): void {
 export function appendFileSync(
   pathOrRid: string | number | URL,
   data: string,
-  options?: string | FileOptions
+  options?: string | WriteFileOptions
 ): void {
   let rid = -1;
 
@@ -110,7 +115,7 @@ export function appendFileSync(
 }
 
 function validateEncoding(
-  encodingOption: string | FileOptions | undefined
+  encodingOption: string | WriteFileOptions | undefined
 ): void {
   if (!encodingOption) return;
 
@@ -122,80 +127,3 @@ function validateEncoding(
     throw new Error("Only 'utf8' encoding is currently supported");
   }
 }
-
-function getOpenOptions(flag: string | undefined): Deno.OpenOptions {
-  if (!flag) {
-    return { create: true, append: true };
-  }
-
-  let openOptions: Deno.OpenOptions;
-  switch (flag) {
-    case "a": {
-      // 'a': Open file for appending. The file is created if it does not exist.
-      openOptions = { create: true, append: true };
-      break;
-    }
-    case "ax": {
-      // 'ax': Like 'a' but fails if the path exists.
-      openOptions = { createNew: true, write: true, append: true };
-      break;
-    }
-    case "a+": {
-      // 'a+': Open file for reading and appending. The file is created if it does not exist.
-      openOptions = { read: true, create: true, append: true };
-      break;
-    }
-    case "ax+": {
-      // 'ax+': Like 'a+' but fails if the path exists.
-      openOptions = { read: true, createNew: true, append: true };
-      break;
-    }
-    case "r": {
-      // 'r': Open file for reading. An exception occurs if the file does not exist.
-      openOptions = { read: true };
-      break;
-    }
-    case "r+": {
-      // 'r+': Open file for reading and writing. An exception occurs if the file does not exist.
-      openOptions = { read: true, write: true };
-      break;
-    }
-    case "w": {
-      // 'w': Open file for writing. The file is created (if it does not exist) or truncated (if it exists).
-      openOptions = { create: true, write: true, truncate: true };
-      break;
-    }
-    case "wx": {
-      // 'wx': Like 'w' but fails if the path exists.
-      openOptions = { createNew: true, write: true };
-      break;
-    }
-    case "w+": {
-      // 'w+': Open file for reading and writing. The file is created (if it does not exist) or truncated (if it exists).
-      openOptions = { create: true, write: true, truncate: true, read: true };
-      break;
-    }
-    case "wx+": {
-      // 'wx+': Like 'w+' but fails if the path exists.
-      openOptions = { createNew: true, write: true, read: true };
-      break;
-    }
-    case "as": {
-      // 'as': Open file for appending in synchronous mode. The file is created if it does not exist.
-      openOptions = { create: true, append: true };
-    }
-    case "as+": {
-      // 'as+': Open file for reading and appending in synchronous mode. The file is created if it does not exist.
-      openOptions = { create: true, read: true, append: true };
-    }
-    case "rs+": {
-      // 'rs+': Open file for reading and writing in synchronous mode. Instructs the operating system to bypass the local file system cache.
-      openOptions = { create: true, read: true, write: true };
-    }
-    default: {
-      throw new Error(`Unrecognized file system flag: ${flag}`);
-    }
-  }
-
-  return openOptions;
-}
diff --git a/std/node/_fs/_fs_common.ts b/std/node/_fs/_fs_common.ts
index ebdd28d64..1f00bc481 100644
--- a/std/node/_fs/_fs_common.ts
+++ b/std/node/_fs/_fs_common.ts
@@ -1,21 +1,137 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
 
-export type CallbackWithError = (err?: Error) => void;
+import { notImplemented } from "../_utils.ts";
+
+export type CallbackWithError = (err?: Error | null) => void;
 
 export interface FileOptions {
   encoding?: string;
-  mode?: number;
   flag?: string;
 }
 
+export interface WriteFileOptions extends FileOptions {
+  mode?: number;
+}
+
 export function isFileOptions(
-  fileOptions: string | FileOptions | undefined
+  fileOptions: string | WriteFileOptions | undefined
 ): fileOptions is FileOptions {
   if (!fileOptions) return false;
 
   return (
     (fileOptions as FileOptions).encoding != undefined ||
     (fileOptions as FileOptions).flag != undefined ||
-    (fileOptions as FileOptions).mode != undefined
+    (fileOptions as WriteFileOptions).mode != undefined
   );
 }
+
+export function getEncoding(
+  optOrCallback?: FileOptions | WriteFileOptions | Function | string
+): string | null {
+  if (!optOrCallback || typeof optOrCallback === "function") {
+    return null;
+  }
+
+  const encoding =
+    typeof optOrCallback === "string" ? optOrCallback : optOrCallback.encoding;
+  if (!encoding) return null;
+  if (encoding === "utf8" || encoding === "utf-8") {
+    return "utf8";
+  }
+  if (encoding === "buffer") {
+    return "buffer";
+  }
+
+  const notImplementedEncodings = [
+    "utf16le",
+    "latin1",
+    "base64",
+    "hex",
+    "ascii",
+    "binary",
+    "ucs2",
+  ];
+
+  if (notImplementedEncodings.includes(encoding)) {
+    notImplemented(`"${encoding}" encoding`);
+  }
+
+  throw new Error(`The value "${encoding}" is invalid for option "encoding"`);
+}
+
+export function getOpenOptions(flag: string | undefined): Deno.OpenOptions {
+  if (!flag) {
+    return { create: true, append: true };
+  }
+
+  let openOptions: Deno.OpenOptions;
+  switch (flag) {
+    case "a": {
+      // 'a': Open file for appending. The file is created if it does not exist.
+      openOptions = { create: true, append: true };
+      break;
+    }
+    case "ax": {
+      // 'ax': Like 'a' but fails if the path exists.
+      openOptions = { createNew: true, write: true, append: true };
+      break;
+    }
+    case "a+": {
+      // 'a+': Open file for reading and appending. The file is created if it does not exist.
+      openOptions = { read: true, create: true, append: true };
+      break;
+    }
+    case "ax+": {
+      // 'ax+': Like 'a+' but fails if the path exists.
+      openOptions = { read: true, createNew: true, append: true };
+      break;
+    }
+    case "r": {
+      // 'r': Open file for reading. An exception occurs if the file does not exist.
+      openOptions = { read: true };
+      break;
+    }
+    case "r+": {
+      // 'r+': Open file for reading and writing. An exception occurs if the file does not exist.
+      openOptions = { read: true, write: true };
+      break;
+    }
+    case "w": {
+      // 'w': Open file for writing. The file is created (if it does not exist) or truncated (if it exists).
+      openOptions = { create: true, write: true, truncate: true };
+      break;
+    }
+    case "wx": {
+      // 'wx': Like 'w' but fails if the path exists.
+      openOptions = { createNew: true, write: true };
+      break;
+    }
+    case "w+": {
+      // 'w+': Open file for reading and writing. The file is created (if it does not exist) or truncated (if it exists).
+      openOptions = { create: true, write: true, truncate: true, read: true };
+      break;
+    }
+    case "wx+": {
+      // 'wx+': Like 'w+' but fails if the path exists.
+      openOptions = { createNew: true, write: true, read: true };
+      break;
+    }
+    case "as": {
+      // 'as': Open file for appending in synchronous mode. The file is created if it does not exist.
+      openOptions = { create: true, append: true };
+    }
+    case "as+": {
+      // 'as+': Open file for reading and appending in synchronous mode. The file is created if it does not exist.
+      openOptions = { create: true, read: true, append: true };
+    }
+    case "rs+": {
+      // 'rs+': Open file for reading and writing in synchronous mode. Instructs the operating system to bypass the local file system cache.
+      openOptions = { create: true, read: true, write: true };
+    }
+    default: {
+      throw new Error(`Unrecognized file system flag: ${flag}`);
+    }
+  }
+
+  return openOptions;
+}
diff --git a/std/node/_fs/_fs_copy_test.ts b/std/node/_fs/_fs_copy_test.ts
index 45e7e9372..9a27f7a83 100644
--- a/std/node/_fs/_fs_copy_test.ts
+++ b/std/node/_fs/_fs_copy_test.ts
@@ -12,7 +12,7 @@ test({
   fn: async () => {
     const srouceFile = Deno.makeTempFileSync();
     const err = await new Promise((resolve) => {
-      copyFile(srouceFile, destFile, (err: Error | undefined) => resolve(err));
+      copyFile(srouceFile, destFile, (err?: Error | null) => resolve(err));
     });
     assert(!err);
     assert(existsSync(destFile));
diff --git a/std/node/_fs/_fs_readFile.ts b/std/node/_fs/_fs_readFile.ts
index 8d3c96db0..6021c84e0 100644
--- a/std/node/_fs/_fs_readFile.ts
+++ b/std/node/_fs/_fs_readFile.ts
@@ -1,10 +1,8 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
 
-import {
-  notImplemented,
-  intoCallbackAPIWithIntercept,
-  MaybeEmpty,
-} from "../_utils.ts";
+import { intoCallbackAPIWithIntercept, MaybeEmpty } from "../_utils.ts";
+
+import { getEncoding, FileOptions } from "./_fs_common.ts";
 import { fromFileUrl } from "../path.ts";
 
 const { readFile: denoReadFile, readFileSync: denoReadFileSync } = Deno;
@@ -14,33 +12,6 @@ type ReadFileCallback = (
   data: MaybeEmpty<string | Uint8Array>
 ) => void;
 
-interface ReadFileOptions {
-  encoding?: string | null;
-  flag?: string;
-}
-
-function getEncoding(
-  optOrCallback?: ReadFileOptions | ReadFileCallback
-): string | null {
-  if (!optOrCallback || typeof optOrCallback === "function") {
-    return null;
-  } else {
-    if (optOrCallback.encoding) {
-      if (
-        optOrCallback.encoding === "utf8" ||
-        optOrCallback.encoding === "utf-8"
-      ) {
-        return "utf8";
-      } else if (optOrCallback.encoding === "buffer") {
-        return "buffer";
-      } else {
-        notImplemented();
-      }
-    }
-    return null;
-  }
-}
-
 function maybeDecode(
   data: Uint8Array,
   encoding: string | null
@@ -53,7 +24,7 @@ function maybeDecode(
 
 export function readFile(
   path: string | URL,
-  optOrCallback: ReadFileCallback | ReadFileOptions,
+  optOrCallback: ReadFileCallback | FileOptions,
   callback?: ReadFileCallback
 ): void {
   path = path instanceof URL ? fromFileUrl(path) : path;
@@ -76,7 +47,7 @@ export function readFile(
 
 export function readFileSync(
   path: string | URL,
-  opt?: ReadFileOptions
+  opt?: FileOptions
 ): string | Uint8Array {
   path = path instanceof URL ? fromFileUrl(path) : path;
   return maybeDecode(denoReadFileSync(path), getEncoding(opt));
diff --git a/std/node/_fs/_fs_writeFile.ts b/std/node/_fs/_fs_writeFile.ts
new file mode 100644
index 000000000..c9f7fe125
--- /dev/null
+++ b/std/node/_fs/_fs_writeFile.ts
@@ -0,0 +1,65 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+import { notImplemented } from "../_utils.ts";
+
+import {
+  WriteFileOptions,
+  CallbackWithError,
+  isFileOptions,
+  getEncoding,
+  getOpenOptions,
+} from "./_fs_common.ts";
+
+export function writeFile(
+  pathOrRid: string | number,
+  data: string | Uint8Array,
+  optOrCallback: string | CallbackWithError | WriteFileOptions | undefined,
+  callback?: CallbackWithError
+): void {
+  const callbackFn: CallbackWithError | undefined =
+    optOrCallback instanceof Function ? optOrCallback : callback;
+  const options: string | WriteFileOptions | undefined =
+    optOrCallback instanceof Function ? undefined : optOrCallback;
+
+  if (!callbackFn) {
+    throw new TypeError("Callback must be a function.");
+  }
+
+  const flag: string | undefined = isFileOptions(options)
+    ? options.flag
+    : undefined;
+
+  const mode: number | undefined = isFileOptions(options)
+    ? options.mode
+    : undefined;
+
+  const encoding = getEncoding(options) || "utf8";
+  const openOptions = getOpenOptions(flag || "w");
+
+  if (typeof data === "string" && encoding === "utf8")
+    data = new TextEncoder().encode(data) as Uint8Array;
+
+  const isRid = typeof pathOrRid === "number";
+  let file;
+
+  let error: Error | null = null;
+  (async (): Promise<void> => {
+    try {
+      file = isRid
+        ? new Deno.File(pathOrRid as number)
+        : await Deno.open(pathOrRid as string, openOptions);
+
+      if (!isRid && mode) {
+        if (Deno.build.os === "windows") notImplemented(`"mode" on Windows`);
+        await Deno.chmod(pathOrRid as string, mode);
+      }
+
+      await Deno.writeAll(file, data as Uint8Array);
+    } catch (e) {
+      error = e;
+    } finally {
+      // Make sure to close resource
+      if (!isRid && file) file.close();
+      callbackFn(error);
+    }
+  })();
+}
diff --git a/std/node/_fs/_fs_writeFile_test.ts b/std/node/_fs/_fs_writeFile_test.ts
new file mode 100644
index 000000000..9b40a1fff
--- /dev/null
+++ b/std/node/_fs/_fs_writeFile_test.ts
@@ -0,0 +1,180 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+const { test } = Deno;
+
+import {
+  assert,
+  assertEquals,
+  assertNotEquals,
+  assertThrows,
+  assertThrowsAsync,
+} from "../../testing/asserts.ts";
+import { writeFile } from "./_fs_writeFile.ts";
+
+const decoder = new TextDecoder("utf-8");
+
+test("Invalid encoding results in error()", function fn() {
+  assertThrows(
+    () => {
+      writeFile("some/path", "some data", "utf8");
+    },
+    TypeError,
+    "Callback must be a function."
+  );
+});
+
+test("Invalid encoding results in error()", function testEncodingErrors() {
+  assertThrows(
+    () => {
+      writeFile("some/path", "some data", "made-up-encoding", () => {});
+    },
+    Error,
+    `The value "made-up-encoding" is invalid for option "encoding"`
+  );
+  assertThrows(
+    () => {
+      writeFile(
+        "some/path",
+        "some data",
+        {
+          encoding: "made-up-encoding",
+        },
+        () => {}
+      );
+    },
+    Error,
+    `The value "made-up-encoding" is invalid for option "encoding"`
+  );
+});
+
+test("Unsupported encoding results in error()", function testUnsupportedEncoding() {
+  assertThrows(
+    () => {
+      writeFile("some/path", "some data", "hex", () => {});
+    },
+    Error,
+    `Not implemented: "hex" encoding`
+  );
+  assertThrows(
+    () => {
+      writeFile(
+        "some/path",
+        "some data",
+        {
+          encoding: "base64",
+        },
+        () => {}
+      );
+    },
+    Error,
+    `Not implemented: "base64" encoding`
+  );
+});
+
+test("Data is written to correct rid", async function testCorrectWriteUsingRid() {
+  const tempFile: string = await Deno.makeTempFile();
+  const file: Deno.File = await Deno.open(tempFile, {
+    create: true,
+    write: true,
+    read: true,
+  });
+
+  await new Promise((resolve, reject) => {
+    writeFile(file.rid, "hello world", (err) => {
+      if (err) return reject(err);
+      resolve();
+    });
+  });
+  Deno.close(file.rid);
+
+  const data = await Deno.readFile(tempFile);
+  await Deno.remove(tempFile);
+  assertEquals(decoder.decode(data), "hello world");
+});
+
+test("Data is written to correct rid", async function testCorrectWriteUsingRid() {
+  const tempFile: string = await Deno.makeTempFile();
+  const file: Deno.File = await Deno.open(tempFile, {
+    create: true,
+    write: true,
+    read: true,
+  });
+
+  await new Promise((resolve, reject) => {
+    writeFile(file.rid, "hello world", (err) => {
+      if (err) return reject(err);
+      resolve();
+    });
+  });
+  Deno.close(file.rid);
+
+  const data = await Deno.readFile(tempFile);
+  await Deno.remove(tempFile);
+  assertEquals(decoder.decode(data), "hello world");
+});
+
+test("Data is written to correct file", async function testCorrectWriteUsingPath() {
+  const res = await new Promise((resolve) => {
+    writeFile("_fs_writeFile_test_file.txt", "hello world", resolve);
+  });
+
+  const data = await Deno.readFile("_fs_writeFile_test_file.txt");
+  await Deno.remove("_fs_writeFile_test_file.txt");
+  assertEquals(res, null);
+  assertEquals(decoder.decode(data), "hello world");
+});
+
+test("Mode is correctly set", async function testCorrectFileMode() {
+  if (Deno.build.os === "windows") return;
+  const filename = "_fs_writeFile_test_file.txt";
+
+  const res = await new Promise((resolve) => {
+    writeFile(filename, "hello world", { mode: 0o777 }, resolve);
+  });
+
+  const fileInfo = await Deno.stat(filename);
+  await Deno.remove(filename);
+  assertEquals(res, null);
+  assert(fileInfo && fileInfo.mode);
+  assertEquals(fileInfo.mode & 0o777, 0o777);
+});
+
+test("Mode is not set when rid is passed", async function testCorrectFileModeRid() {
+  if (Deno.build.os === "windows") return;
+
+  const filename: string = await Deno.makeTempFile();
+  const file: Deno.File = await Deno.open(filename, {
+    create: true,
+    write: true,
+    read: true,
+  });
+
+  await new Promise((resolve, reject) => {
+    writeFile(file.rid, "hello world", { mode: 0o777 }, (err) => {
+      if (err) return reject(err);
+      resolve();
+    });
+  });
+  Deno.close(file.rid);
+
+  const fileInfo = await Deno.stat(filename);
+  await Deno.remove(filename);
+  assert(fileInfo.mode);
+  assertNotEquals(fileInfo.mode & 0o777, 0o777);
+});
+
+test("Mode is not implemented on windows", function testModeNotImplementedWindows(): void {
+  if (Deno.build.os !== "windows") return;
+
+  assertThrowsAsync(
+    () => {
+      return new Promise((resolve, reject) => {
+        writeFile("fail.txt", "some data", { mode: 0o777 }, (err) => {
+          if (err) return reject(err);
+          resolve();
+        });
+      });
+    },
+    Error,
+    `Not implemented: "mode" on Windows`
+  );
+});
diff --git a/std/node/_fs/promises/_fs_writeFile.ts b/std/node/_fs/promises/_fs_writeFile.ts
new file mode 100644
index 000000000..a8f9586a2
--- /dev/null
+++ b/std/node/_fs/promises/_fs_writeFile.ts
@@ -0,0 +1,17 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+import { WriteFileOptions } from "../_fs_common.ts";
+
+import { writeFile as writeFileCallback } from "../_fs_writeFile.ts";
+
+export function writeFile(
+  pathOrRid: string | number,
+  data: string | Uint8Array,
+  options?: string | WriteFileOptions
+): Promise<void> {
+  return new Promise((resolve, reject) => {
+    writeFileCallback(pathOrRid, data, options, (err?: Error | null) => {
+      if (err) return reject(err);
+      resolve();
+    });
+  });
+}
diff --git a/std/node/_fs/promises/_fs_writeFile_test.ts b/std/node/_fs/promises/_fs_writeFile_test.ts
new file mode 100644
index 000000000..c67a7947a
--- /dev/null
+++ b/std/node/_fs/promises/_fs_writeFile_test.ts
@@ -0,0 +1,119 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+const { test } = Deno;
+
+import {
+  assert,
+  assertEquals,
+  assertNotEquals,
+  assertThrowsAsync,
+} from "../../../testing/asserts.ts";
+import { writeFile } from "./_fs_writeFile.ts";
+
+const decoder = new TextDecoder("utf-8");
+
+test("Invalid encoding results in error()", function testEncodingErrors() {
+  assertThrowsAsync(
+    async () => {
+      await writeFile("some/path", "some data", "made-up-encoding");
+    },
+    Error,
+    `The value "made-up-encoding" is invalid for option "encoding"`
+  );
+  assertThrowsAsync(
+    async () => {
+      await writeFile("some/path", "some data", {
+        encoding: "made-up-encoding",
+      });
+    },
+    Error,
+    `The value "made-up-encoding" is invalid for option "encoding"`
+  );
+});
+
+test("Unsupported encoding results in error()", function testUnsupportedEncoding() {
+  assertThrowsAsync(
+    async () => {
+      await writeFile("some/path", "some data", "hex");
+    },
+    Error,
+    `Not implemented: "hex" encoding`
+  );
+  assertThrowsAsync(
+    async () => {
+      await writeFile("some/path", "some data", {
+        encoding: "base64",
+      });
+    },
+    Error,
+    `Not implemented: "base64" encoding`
+  );
+});
+
+test("Data is written to correct rid", async function testCorrectWriteUsingRid() {
+  const tempFile: string = await Deno.makeTempFile();
+  const file: Deno.File = await Deno.open(tempFile, {
+    create: true,
+    write: true,
+    read: true,
+  });
+
+  await writeFile(file.rid, "hello world");
+  Deno.close(file.rid);
+
+  const data = await Deno.readFile(tempFile);
+  await Deno.remove(tempFile);
+  assertEquals(decoder.decode(data), "hello world");
+});
+
+test("Data is written to correct file", async function testCorrectWriteUsingPath() {
+  const openResourcesBeforeWrite: Deno.ResourceMap = Deno.resources();
+
+  await writeFile("_fs_writeFile_test_file.txt", "hello world");
+
+  assertEquals(Deno.resources(), openResourcesBeforeWrite);
+  const data = await Deno.readFile("_fs_writeFile_test_file.txt");
+  await Deno.remove("_fs_writeFile_test_file.txt");
+  assertEquals(decoder.decode(data), "hello world");
+});
+
+test("Mode is correctly set", async function testCorrectFileMode() {
+  if (Deno.build.os === "windows") return;
+  const filename = "_fs_writeFile_test_file.txt";
+  await writeFile(filename, "hello world", { mode: 0o777 });
+
+  const fileInfo = await Deno.stat(filename);
+  await Deno.remove(filename);
+  assert(fileInfo && fileInfo.mode);
+  assertEquals(fileInfo.mode & 0o777, 0o777);
+});
+
+test("Mode is not set when rid is passed", async function testCorrectFileModeRid() {
+  if (Deno.build.os === "windows") return;
+
+  const filename: string = await Deno.makeTempFile();
+  const file: Deno.File = await Deno.open(filename, {
+    create: true,
+    write: true,
+    read: true,
+  });
+
+  await writeFile(file.rid, "hello world", { mode: 0o777 });
+  Deno.close(file.rid);
+
+  const fileInfo = await Deno.stat(filename);
+  await Deno.remove(filename);
+  assert(fileInfo.mode);
+  assertNotEquals(fileInfo.mode & 0o777, 0o777);
+});
+
+test("Mode is not implemented on windows", function testModeNotImplementedWindows(): void {
+  if (Deno.build.os !== "windows") return;
+
+  assertThrowsAsync(
+    async () => {
+      await writeFile("fail.txt", "some data", { mode: 0o777 });
+    },
+    Error,
+    `Not implemented: "mode" on Windows`
+  );
+});
diff --git a/std/node/_fs/promises/mod.ts b/std/node/_fs/promises/mod.ts
new file mode 100644
index 000000000..3cb81a422
--- /dev/null
+++ b/std/node/_fs/promises/mod.ts
@@ -0,0 +1 @@
+export { writeFile } from "./_fs_writeFile.ts";
diff --git a/std/node/fs.ts b/std/node/fs.ts
index 343786e24..737f2a0e9 100755
--- a/std/node/fs.ts
+++ b/std/node/fs.ts
@@ -11,6 +11,8 @@ import { readlink, readlinkSync } from "./_fs/_fs_readlink.ts";
 import { exists, existsSync } from "./_fs/_fs_exists.ts";
 import { mkdir, mkdirSync } from "./_fs/_fs_mkdir.ts";
 import { copyFile, copyFileSync } from "./_fs/_fs_copy.ts";
+import { writeFile } from "./_fs/_fs_writeFile.ts";
+import * as promises from "./_fs/promises/mod.ts";
 
 export {
   access,
@@ -34,4 +36,6 @@ export {
   readlinkSync,
   mkdir,
   mkdirSync,
+  writeFile,
+  promises,
 };