From a6b79ca2bf3f110a7d161ea25ef71d09f3419c5c Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Fri, 15 Dec 2023 11:18:51 +0100
Subject: [PATCH] fix: use prototypeless objects for field-to-type mappings

Fixes: https://github.com/mongodb-js/mongodb-schema/issues/211
---
 src/schema-analyzer.ts         | 6 +++---
 test/basic.test.ts             | 7 +++++--
 test/mixed-type-nested.test.ts | 5 +++--
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/src/schema-analyzer.ts b/src/schema-analyzer.ts
index 7d641cb..9280a39 100644
--- a/src/schema-analyzer.ts
+++ b/src/schema-analyzer.ts
@@ -1,6 +1,6 @@
 
 import Reservoir from 'reservoir';
-import type {
+import {
   Document,
   ObjectId,
   MinKey,
@@ -432,7 +432,7 @@ export class SchemaAnalyzer {
   options: SchemaParseOptions;
   documentsAnalyzed = 0;
   schemaAnalysisRoot: SchemaAnalysisRoot = {
-    fields: {},
+    fields: Object.create(null),
     count: 0
   };
 
@@ -513,7 +513,7 @@ export class SchemaAnalyzer {
         (value as BSONValue[]).forEach((v: BSONValue) => addToType(path, v, type.types));
       } else if (isDocumentType(type)) {
         // Recurse into nested documents by calling `addToField` for all sub-fields.
-        type.fields = type.fields ?? {};
+        type.fields = type.fields ?? Object.create(null);
         Object.entries(value as Document).forEach(
           ([fieldName, v]) => addToField(fieldName, [...path, fieldName], v, type.fields)
         );
diff --git a/test/basic.test.ts b/test/basic.test.ts
index 6f01c5d..bd60159 100644
--- a/test/basic.test.ts
+++ b/test/basic.test.ts
@@ -19,7 +19,8 @@ describe('using only basic fields', function() {
       last_address_longitude: null,
       created_at: new Date(),
       length: 29,
-      'name[]': 'Annabeth Frankie'
+      'name[]': 'Annabeth Frankie',
+      toString: 42
     }
   ];
 
@@ -38,7 +39,8 @@ describe('using only basic fields', function() {
       'name',
       'stats_friends',
       'twitter_username',
-      'name[]'
+      'name[]',
+      'toString'
     ];
     assert.deepEqual(users.fields.map(v => v.name).sort(), fieldNames.sort());
   });
@@ -59,5 +61,6 @@ describe('using only basic fields', function() {
     assert.equal(users.fields.find(v => v.name === 'name')?.type, 'String');
     assert.equal(users.fields.find(v => v.name === 'stats_friends')?.type, 'Number');
     assert.equal(users.fields.find(v => v.name === 'twitter_username')?.type, 'String');
+    assert.equal(users.fields.find(v => v.name === 'toString')?.type, 'Number');
   });
 });
diff --git a/test/mixed-type-nested.test.ts b/test/mixed-type-nested.test.ts
index e52551c..ef2d9b5 100644
--- a/test/mixed-type-nested.test.ts
+++ b/test/mixed-type-nested.test.ts
@@ -30,10 +30,11 @@ describe('mixed types nested', function() {
     {
       _id: 5,
       address: {
-        valid: true
+        valid: true,
+        toString: { value: false }
       }
     }
-  ];
+  ] as const;
 
   let schema: Schema;
   let valid: SchemaField | undefined;