Search results flicker back to the previous query

Problem Description

src/searchController.js runs a search on every keystroke. Users report that results occasionally snap back to what they typed a moment ago: a slow request for an earlier query lands after a fast request for the current one and overwrites it.

The controller already carries a guard for this. Nothing tests it. The existing test resolves one request at a time, so the out-of-order case never occurs.

Output Specification

Add src/searchController.test.js proving that a response arriving for a superseded query does not replace the current results, and that the ordering under test is decided by the test rather than by how fast the machine happens to be.

Run npm test before you finish; it must pass.

Leave src/searchController.basic.test.js in place.

Input Files

Extract the following files before beginning.

=============== FILE: package.json =============== { "name": "search-ui", "version": "0.6.0", "private": true, "scripts": { "test": "node --test" } }

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

function createSearchController(search) { let latestSequence = 0; let state = { query: null, results: [] };

return { async run(query) { latestSequence += 1; const sequence = latestSequence; const results = await search(query); if (sequence !== latestSequence) { return { applied: false, reason: 'SUPERSEDED' }; } state = { query, results }; return { applied: true, reason: null }; }, snapshot() { return state; }, }; }

module.exports = { createSearchController };

=============== FILE: src/searchController.basic.test.js =============== 'use strict';

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

test('applies results for a single query', async () => { const controller = createSearchController(async (query) => [${query}-hit]);

await controller.run('apple');

assert.deepEqual(controller.snapshot(), { query: 'apple', results: ['apple-hit'] }); });