fs: default open/openSync flags argument to 'r'

Make fs.open() and fs.openSync() more economic to use by making the
flags argument optional. You can now write:

    fs.open(file, cb)

Instead of the more verbose:

    fs.open(file, 'r', cb)

This idiom is already supported by functions like fs.readFile().

PR-URL: https://github.com/nodejs/node/pull/23767
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

1 files changed, 12 insertions, 7 deletions

diff --git a/lib/fs.js b/lib/fs.js
index bf964f5e99..89c005375f 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -345,7 +345,7 @@ function tryReadSync(fd, isUserFd, buffer, pos, len) {
 function readFileSync(path, options) {
   options = getOptions(options, { flag: 'r' });
   const isUserFd = isFd(path); // file descriptor ownership
-  const fd = isUserFd ? path : fs.openSync(path, options.flag || 'r', 0o666);
+  const fd = isUserFd ? path : fs.openSync(path, options.flag, 0o666);
 
   const stats = tryStatSync(fd, isUserFd);
   const size = isFileType(stats, S_IFREG) ? stats[8] : 0;
@@ -411,14 +411,19 @@ function closeSync(fd) {
 function open(path, flags, mode, callback) {
   path = toPathIfFileURL(path);
   validatePath(path);
-  const flagsNumber = stringToFlags(flags);
-  if (arguments.length < 4) {
-    callback = makeCallback(mode);
+  if (arguments.length < 3) {
+    callback = flags;
+    flags = 'r';
     mode = 0o666;
-  } else {
+  } else if (arguments.length === 3) {
+    callback = mode;
+    mode = 0o666;
+  }
+  const flagsNumber = stringToFlags(flags);
+  if (arguments.length >= 4) {
     mode = validateMode(mode, 'mode', 0o666);
-    callback = makeCallback(callback);
   }
+  callback = makeCallback(callback);
 
   const req = new FSReqCallback();
   req.oncomplete = callback;
@@ -433,7 +438,7 @@ function open(path, flags, mode, callback) {
 function openSync(path, flags, mode) {
   path = toPathIfFileURL(path);
   validatePath(path);
-  const flagsNumber = stringToFlags(flags);
+  const flagsNumber = stringToFlags(flags || 'r');
   mode = validateMode(mode, 'mode', 0o666);
 
   const ctx = { path };