some progress

node_modules/mongoose/lib/helpers/projection/isPathExcluded.js

@@ -0,0 +1,40 @@
+'use strict';
+
+const isDefiningProjection = require('./isDefiningProjection');
+
+/**
+ * Determines if `path` is excluded by `projection`
+ *
+ * @param {Object} projection
+ * @param {String} path
+ * @return {Boolean}
+ * @api private
+ */
+
+module.exports = function isPathExcluded(projection, path) {
+  if (projection == null) {
+    return false;
+  }
+
+  if (path === '_id') {
+    return projection._id === 0;
+  }
+
+  const paths = Object.keys(projection);
+  let type = null;
+
+  for (const _path of paths) {
+    if (isDefiningProjection(projection[_path])) {
+      type = projection[path] === 1 ? 'inclusive' : 'exclusive';
+      break;
+    }
+  }
+
+  if (type === 'inclusive') {
+    return projection[path] !== 1;
+  }
+  if (type === 'exclusive') {
+    return projection[path] === 0;
+  }
+  return false;
+};