fs: tests and docs for additional modes as and as+

Author: SirR4T

doc/api/fs.md

@@ -2019,11 +2019,17 @@ The file is created if it does not exist.
 
 * `'ax'` - Like `'a'` but fails if `path` exists.
 
+* `'as'` - Open file for appending in synchronous mode.
+The file is created if it does not exist.
+
 * `'a+'` - Open file for reading and appending.
 The file is created if it does not exist.
 
 * `'ax+'` - Like `'a+'` but fails if `path` exists.
 
+* `'as+'` - Open file for reading and appending in synchronous mode.
+The file is created if it does not exist.
+
 `mode` sets the file mode (permission and sticky bits), but only if the file was
 created. It defaults to `0o666` (readable and writable).
 
@@ -3907,11 +3913,17 @@ The file is created if it does not exist.
 
 * `'ax'` - Like `'a'` but fails if `path` exists.
 
+* `'as'` - Open file for appending in synchronous mode.
+The file is created if it does not exist.
+
 * `'a+'` - Open file for reading and appending.
 The file is created if it does not exist.
 
 * `'ax+'` - Like `'a+'` but fails if `path` exists.
 
+* `'as+'` - Open file for reading and appending in synchronous mode.
+The file is created if it does not exist.
+
 `mode` sets the file mode (permission and sticky bits), but only if the file was
 created. It defaults to `0o666` (readable and writable).
 

test/parallel/test-fs-open-flags.js

@@ -56,8 +56,12 @@ assert.strictEqual(stringToFlags('wx+'), O_TRUNC | O_CREAT | O_RDWR | O_EXCL);
 assert.strictEqual(stringToFlags('xw+'), O_TRUNC | O_CREAT | O_RDWR | O_EXCL);
 assert.strictEqual(stringToFlags('ax'), O_APPEND | O_CREAT | O_WRONLY | O_EXCL);
 assert.strictEqual(stringToFlags('xa'), O_APPEND | O_CREAT | O_WRONLY | O_EXCL);
+assert.strictEqual(stringToFlags('as'), O_APPEND | O_CREAT | O_WRONLY | O_SYNC);
+assert.strictEqual(stringToFlags('sa'), O_APPEND | O_CREAT | O_WRONLY | O_SYNC);
 assert.strictEqual(stringToFlags('ax+'), O_APPEND | O_CREAT | O_RDWR | O_EXCL);
 assert.strictEqual(stringToFlags('xa+'), O_APPEND | O_CREAT | O_RDWR | O_EXCL);
+assert.strictEqual(stringToFlags('as+'), O_APPEND | O_CREAT | O_RDWR | O_SYNC);
+assert.strictEqual(stringToFlags('sa+'), O_APPEND | O_CREAT | O_RDWR | O_SYNC);
 
 ('+ +a +r +w rw wa war raw r++ a++ w++ x +x x+ rx rx+ wxx wax xwx xxx')
   .split(' ')