fix: coerce integerValue fields to JS number when reading documents

.changeset/integer-value-coercion.md

@@ -0,0 +1,9 @@
+---
+'fireworkers': minor
+---
+
+fix: coerce `integerValue` fields to JS `number` when reading documents.
+
+Firestore's REST API serializes `integerValue` as a string to preserve int64 precision. Previously, fireworkers returned the raw string; it now coerces to `number` to match the Firebase Admin SDK.
+
+**BREAKING for consumers relying on `integerValue` fields being returned as strings.** This only affects data written by other clients (Admin SDK, console, other languages) — fireworkers writes all numbers as `doubleValue`, so round-trips within fireworkers were never affected. Values beyond `Number.MAX_SAFE_INTEGER` (2^53 − 1) will lose precision; if you need full int64 support, read the raw document via the REST API directly.

src/fields.test.ts

@@ -0,0 +1,133 @@
+import { beforeAll, beforeEach, describe, expect, it } from 'vitest';
+
+import { clearFirestore, initDb, TEST_PROJECT_ID } from '../tests/unit/helpers';
+import { extract_fields_from_document } from './fields';
+import { get } from './get';
+import type { DB, Document } from './types';
+
+const EMULATOR_HOST = process.env.FIRESTORE_EMULATOR_HOST ?? '127.0.0.1:8080';
+
+/**
+ * Writes a raw Firestore document to the emulator, bypassing fireworkers so
+ * we can produce an `integerValue` field (fireworkers always writes numbers
+ * as `doubleValue`).
+ */
+const writeRawDocument = async (
+  collection: string,
+  documentId: string,
+  fields: Document['fields']
+): Promise<void> => {
+  const url = `http://${EMULATOR_HOST}/v1/projects/${TEST_PROJECT_ID}/databases/(default)/documents/${collection}?documentId=${documentId}`;
+  const response = await fetch(url, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ fields }),
+  });
+
+  if (!response.ok) {
+    throw new Error(`Failed to seed document: ${response.status} ${await response.text()}`);
+  }
+};
+
+describe('extract_fields_from_document', () => {
+  it('coerces integerValue strings to JS numbers', () => {
+    const document: Document = {
+      name: 'projects/test/databases/(default)/documents/todos/abc',
+      fields: {
+        updatedTimestamp: { integerValue: '1730404244' },
+      },
+    };
+
+    const extracted = extract_fields_from_document<{ updatedTimestamp: number }>(document);
+
+    expect(extracted.fields.updatedTimestamp).toBe(1730404244);
+    expect(typeof extracted.fields.updatedTimestamp).toBe('number');
+  });
+
+  it('maps each primitive type to the correct JS type', () => {
+    const document: Document = {
+      name: 'projects/test/databases/(default)/documents/mix/doc',
+      fields: {
+        int: { integerValue: '42' },
+        double: { doubleValue: 3.14 },
+        str: { stringValue: 'hello' },
+        bool: { booleanValue: true },
+        missing: { nullValue: 'NULL_VALUE' },
+      },
+    };
+
+    const extracted = extract_fields_from_document<{
+      int: number;
+      double: number;
+      str: string;
+      bool: boolean;
+      missing: null;
+    }>(document);
+
+    expect(extracted.fields.int).toBe(42);
+    expect(typeof extracted.fields.int).toBe('number');
+    expect(extracted.fields.double).toBe(3.14);
+    expect(extracted.fields.str).toBe('hello');
+    expect(extracted.fields.bool).toBe(true);
+    expect(extracted.fields.missing).toBe('NULL_VALUE');
+  });
+
+  it('coerces integerValue nested inside arrayValue and mapValue', () => {
+    const document: Document = {
+      name: 'projects/test/databases/(default)/documents/nested/doc',
+      fields: {
+        list: {
+          arrayValue: {
+            values: [{ integerValue: '1' }, { integerValue: '2' }],
+          },
+        },
+        meta: {
+          mapValue: {
+            fields: {
+              count: { integerValue: '99' },
+            },
+          },
+        },
+      },
+    };
+
+    const extracted = extract_fields_from_document<{
+      list: number[];
+      meta: { count: number };
+    }>(document);
+
+    expect(extracted.fields.list).toEqual([1, 2]);
+    expect(typeof extracted.fields.list[0]).toBe('number');
+    expect(extracted.fields.meta.count).toBe(99);
+    expect(typeof extracted.fields.meta.count).toBe('number');
+  });
+});
+
+describe('get with integerValue seeded via raw REST (emulator)', () => {
+  let db: DB;
+
+  beforeAll(async () => {
+    db = await initDb();
+  });
+  beforeEach(clearFirestore);
+
+  it('returns integerValue fields as JS numbers', async () => {
+    await writeRawDocument('todos', 'seeded', {
+      updatedTimestamp: { integerValue: '1730404244' },
+      count: { integerValue: '42' },
+      title: { stringValue: 'seeded externally' },
+    });
+
+    const doc = await get<{
+      updatedTimestamp: number;
+      count: number;
+      title: string;
+    }>(db, 'todos', 'seeded');
+
+    expect(doc.fields.updatedTimestamp).toBe(1730404244);
+    expect(typeof doc.fields.updatedTimestamp).toBe('number');
+    expect(doc.fields.count).toBe(42);
+    expect(typeof doc.fields.count).toBe('number');
+    expect(doc.fields.title).toBe('seeded externally');
+  });
+});

src/fields.ts

@@ -115,8 +115,18 @@ const extract_value = (value: Firestore.Value): MappedValue => {
  * Extracts a primitive value from a field object.
  * @param primitiveValues
  */
-const extract_primitive_value = (primitiveValues: PrimitiveValues) =>
-  Object.values(primitiveValues)[0];
+const extract_primitive_value = (primitiveValues: PrimitiveValues) => {
+  const entry = Object.entries(primitiveValues)[0];
+  if (!entry) return undefined;
+
+  const [key, value] = entry;
+
+  // Firestore's REST API returns integerValue as a string to preserve int64
+  // precision. Coerce to number to match the Firebase Admin SDK behavior.
+  if (key === 'integerValue') return Number(value);
+
+  return value;
+};
 
 /**
  * Extracts an array field.