flow like the river

BACK_BACK/node_modules/mongoose/lib/helpers/projection/isExclusive.js

@@ -0,0 +1,34 @@
+'use strict';
+
+const isDefiningProjection = require('./isDefiningProjection');
+
+/*!
+ * ignore
+ */
+
+module.exports = function isExclusive(projection) {
+  if (projection == null) {
+    return null;
+  }
+
+  const keys = Object.keys(projection);
+  let exclude = null;
+
+  if (keys.length === 1 && keys[0] === '_id') {
+    exclude = !projection._id;
+  } else {
+    for (let ki = 0; ki < keys.length; ++ki) {
+      // Does this projection explicitly define inclusion/exclusion?
+      // Explicitly avoid `$meta` and `$slice`
+      const key = keys[ki];
+      if (key !== '_id' && isDefiningProjection(projection[key])) {
+        exclude = (projection[key] != null && typeof projection[key] === 'object') ?
+          isExclusive(projection[key]) :
+          !projection[key];
+        break;
+      }
+    }
+  }
+
+  return exclude;
+};