Settings update trusts the client's types

Problem Description

src/updateSettings.js applies a partial settings update. Each field has a declared type, and the handler rejects anything that does not match.

We shipped a bug where itemsPerPage arrived as the string "25" from an older mobile client and was stored as a string, which broke pagination downstream. The handler does reject it now, but nothing tests that it does - and the same hole exists for the other fields.

Output Specification

Add src/updateSettings.test.js covering the wrong-type rejection for every field this handler accepts, plus the value-level rejections it implements.

Run npm test before you finish; it must pass.

Leave src/updateSettings.happy.test.js in place.

Input Files

Extract the following files before beginning.

=============== FILE: package.json =============== { "name": "user-preferences", "version": "4.1.1", "private": true, "scripts": { "test": "node --test" } }

=============== FILE: src/updateSettings.js =============== 'use strict';

const THEMES = ['light', 'dark', 'system']; const ITEMS_MIN = 5; const ITEMS_MAX = 100;

function updateSettings(current, patch) { if (patch === null || typeof patch !== 'object' || Array.isArray(patch)) { return { ok: false, field: null, code: 'MALFORMED_PATCH' }; }

if ('theme' in patch) { if (typeof patch.theme !== 'string') { return { ok: false, field: 'theme', code: 'WRONG_TYPE' }; } if (!THEMES.includes(patch.theme)) { return { ok: false, field: 'theme', code: 'UNSUPPORTED_VALUE' }; } }

if ('notificationsEnabled' in patch) { if (typeof patch.notificationsEnabled !== 'boolean') { return { ok: false, field: 'notificationsEnabled', code: 'WRONG_TYPE' }; } }

if ('itemsPerPage' in patch) { if (typeof patch.itemsPerPage !== 'number' || !Number.isInteger(patch.itemsPerPage)) { return { ok: false, field: 'itemsPerPage', code: 'WRONG_TYPE' }; } if (patch.itemsPerPage < ITEMS_MIN || patch.itemsPerPage > ITEMS_MAX) { return { ok: false, field: 'itemsPerPage', code: 'OUT_OF_RANGE' }; } }

if ('tags' in patch) { if (!Array.isArray(patch.tags)) { return { ok: false, field: 'tags', code: 'WRONG_TYPE' }; } if (patch.tags.some((tag) => typeof tag !== 'string')) { return { ok: false, field: 'tags', code: 'WRONG_ELEMENT_TYPE' }; } }

return { ok: true, field: null, code: null, settings: { ...current, ...patch } }; }

module.exports = { updateSettings, THEMES, ITEMS_MIN, ITEMS_MAX };

=============== FILE: src/updateSettings.happy.test.js =============== 'use strict';

const test = require('node:test'); const assert = require('node:assert/strict'); const { updateSettings } = require('./updateSettings');

const CURRENT = { theme: 'light', notificationsEnabled: true, itemsPerPage: 25, tags: [] };

test('applies a partial update', () => { const result = updateSettings(CURRENT, { theme: 'dark' }); assert.equal(result.ok, true); assert.equal(result.settings.theme, 'dark'); assert.equal(result.settings.itemsPerPage, 25); });