perf(document): only loop over doc once when shallow cloning re: #14719

lib/document.js

@@ -3868,17 +3868,21 @@ Document.prototype.$toObject = function(options, json) {
   if (hasOnlyPrimitiveValues) {
     // Fast path: if we don't have any nested objects or arrays, we only need a
     // shallow clone.
-    ret = this._doc
-      ? options.minimize ? (minimize({ ...this._doc }) || {}) : { ...this._doc }
-      : {};
-    if (!options.minimize || options.flattenObjectIds) {
-      const keys = Object.keys(ret);
-      for (const key of keys) {
-        // If `minimize` is false, still need to remove undefined keys
-        if (!options.minimize && ret[key] === undefined) {
+    if (this._doc == null) {
+      ret = {};
+    }
+    ret = {};
+    if (this._doc != null) {
+      for (const key of Object.keys(this._doc)) {
+        const value = this._doc[key];
+        if (value instanceof Date) {
+          ret[key] = new Date(value);
+        } else if (value === undefined) {
           delete ret[key];
-        } else if (options.flattenObjectIds && isBsonType(ret[key], 'ObjectId')) {
-          ret[key] = ret[key].toJSON();
+        } else if (options.flattenObjectIds && isBsonType(value, 'ObjectId')) {
+          ret[key] = value.toJSON();
+        } else {
+          ret[key] = value;
         }
       }
     }