some progress

node_modules/mongoose/lib/helpers/query/handleImmutable.js

@@ -0,0 +1,28 @@
+'use strict';
+
+const StrictModeError = require('../../error/strict');
+
+module.exports = function handleImmutable(schematype, strict, obj, key, fullPath, ctx) {
+  if (schematype == null || !schematype.options || !schematype.options.immutable) {
+    return false;
+  }
+  let immutable = schematype.options.immutable;
+
+  if (typeof immutable === 'function') {
+    immutable = immutable.call(ctx, ctx);
+  }
+  if (!immutable) {
+    return false;
+  }
+
+  if (strict === false) {
+    return false;
+  }
+  if (strict === 'throw') {
+    throw new StrictModeError(null,
+      `Field ${fullPath} is immutable and strict = 'throw'`);
+  }
+
+  delete obj[key];
+  return true;
+};