lib: lazy instantiation of fs.Stats dates

The method used has code duplication but is the most performant

PR-URL: https://github.com/nodejs/node/pull/12818
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>

lib/fs.js

@@ -196,13 +196,79 @@ function Stats(
   this.ino = ino;
   this.size = size;
   this.blocks = blocks;
-  this.atime = new Date(atim_msec);
-  this.mtime = new Date(mtim_msec);
-  this.ctime = new Date(ctim_msec);
-  this.birthtime = new Date(birthtim_msec);
+  this._atim_msec = atim_msec;
+  this._mtim_msec = mtim_msec;
+  this._ctim_msec = ctim_msec;
+  this._birthtim_msec = birthtim_msec;
 }
 fs.Stats = Stats;
 
+// defining the properties in this fashion (explicitly with no loop or factory)
+// has been shown to be the most performant on V8 contemp.
+// Ref: https://github.com/nodejs/node/pull/12818
+Object.defineProperties(Stats.prototype, {
+  atime: {
+    configurable: true,
+    enumerable: true,
+    get() {
+      return this._atime !== undefined ?
+          this._atime :
+          (this._atime = new Date(this._atim_msec + 0.5));
+    },
+    set(value) { return this._atime = value; }
+  },
+  mtime: {
+    configurable: true,
+    enumerable: true,
+    get() {
+      return this._mtime !== undefined ?
+          this._mtime :
+          (this._mtime = new Date(this._mtim_msec + 0.5));
+    },
+    set(value) { return this._mtime = value; }
+  },
+  ctime: {
+    configurable: true,
+    enumerable: true,
+    get() {
+      return this._ctime !== undefined ?
+        this._ctime :
+        (this._ctime = new Date(this._ctim_msec + 0.5));
+    },
+    set(value) { return this._ctime = value; }
+  },
+  birthtime: {
+    configurable: true,
+    enumerable: true,
+    get() {
+      return this._birthtime !== undefined ?
+        this._birthtime :
+        (this._birthtime = new Date(this._birthtim_msec + 0.5));
+    },
+    set(value) { return this._birthtime = value; }
+  },
+});
+
+Stats.prototype.toJSON = function toJSON() {
+  return {
+    dev: this.dev,
+    mode: this.mode,
+    nlink: this.nlink,
+    uid: this.uid,
+    gid: this.gid,
+    rdev: this.rdev,
+    blksize: this.blksize,
+    ino: this.ino,
+    size: this.size,
+    blocks: this.blocks,
+    atime: this.atime,
+    ctime: this.ctime,
+    mtime: this.mtime,
+    birthtime: this.birthtime
+  };
+};
+
+
 Stats.prototype._checkModeProperty = function(property) {
   return ((this.mode & S_IFMT) === property);
 };

test/parallel/test-fs-stat.js

@@ -98,5 +98,27 @@ fs.stat(__filename, common.mustCall(function(err, s) {
   console.log(`isSymbolicLink: ${JSON.stringify(s.isSymbolicLink())}`);
   assert.strictEqual(false, s.isSymbolicLink());
 
+  assert.ok(s.atime instanceof Date);
   assert.ok(s.mtime instanceof Date);
+  assert.ok(s.ctime instanceof Date);
+  assert.ok(s.birthtime instanceof Date);
+}));
+
+fs.stat(__filename, common.mustCall(function(err, s) {
+  const json = JSON.parse(JSON.stringify(s));
+  const keys = [
+    'dev', 'mode', 'nlink', 'uid',
+    'gid', 'rdev', 'ino',
+    'size', 'atime', 'mtime',
+    'ctime', 'birthtime'
+  ];
+  if (!common.isWindows) {
+    keys.push('blocks', 'blksize');
+  }
+  keys.forEach(function(k) {
+    assert.ok(
+      json[k] !== undefined && json[k] !== null,
+      k + ' should not be null or undefined'
+    );
+  });
 }));