some progress

node_modules/mongoose/lib/options/PopulateOptions.js

@@ -0,0 +1,36 @@
+'use strict';
+
+const clone = require('../helpers/clone');
+
+class PopulateOptions {
+  constructor(obj) {
+    this._docs = {};
+    this._childDocs = [];
+
+    if (obj == null) {
+      return;
+    }
+    obj = clone(obj);
+    Object.assign(this, obj);
+    if (typeof obj.subPopulate === 'object') {
+      this.populate = obj.subPopulate;
+    }
+
+
+    if (obj.perDocumentLimit != null && obj.limit != null) {
+      throw new Error('Can not use `limit` and `perDocumentLimit` at the same time. Path: `' + obj.path + '`.');
+    }
+  }
+}
+
+/**
+ * The connection used to look up models by name. If not specified, Mongoose
+ * will default to using the connection associated with the model in
+ * `PopulateOptions#model`.
+ *
+ * @memberOf PopulateOptions
+ * @property {Connection} connection
+ * @api public
+ */
+
+module.exports = PopulateOptions;