some progress

node_modules/mongoose/lib/helpers/schema/getPath.js

@@ -0,0 +1,38 @@
+'use strict';
+
+const numberRE = /^\d+$/;
+
+/**
+ * Behaves like `Schema#path()`, except for it also digs into arrays without
+ * needing to put `.0.`, so `getPath(schema, 'docArr.elProp')` works.
+ * @api private
+ */
+
+module.exports = function getPath(schema, path) {
+  let schematype = schema.path(path);
+  if (schematype != null) {
+    return schematype;
+  }
+
+  const pieces = path.split('.');
+  let cur = '';
+  let isArray = false;
+
+  for (const piece of pieces) {
+    if (isArray && numberRE.test(piece)) {
+      continue;
+    }
+    cur = cur.length === 0 ? piece : cur + '.' + piece;
+
+    schematype = schema.path(cur);
+    if (schematype != null && schematype.schema) {
+      schema = schematype.schema;
+      cur = '';
+      if (!isArray && schematype.$isMongooseDocumentArray) {
+        isArray = true;
+      }
+    }
+  }
+
+  return schematype;
+};