Technical Skills

JavaScript Developer Test

Assess JavaScript fundamentals, asynchronous programming, DOM concepts and modern language features.

45 minMedium15 questions15 sections

JavaScript fundamentalsDOM conceptsAsynchronous programmingModern JavaScript syntax

Topics covered

Async UIPromisesEventsSecurityNode.js PerformanceStreamsAsync ErrorsNetworkingState ManagementCachingModulesConcurrency ControlAPI HandlerTestingPerformance

Sample questions

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Async UIMid-level

A search field calls this function on every keystroke: async function search(query) { const response = await fetch(`/api/search?q=${encodeURIComponent(query)}`); const results = await response.json(); render(results); } Users sometimes see results for an older query after typing quickly. Explain the bug and implement a safe approach.

PromisesMid-level

A dashboard uses Promise.all to load profile, invoices and recommendations. Recommendations are optional, but one failure blanks the entire page. Redesign the loading and error handling.

EventsMid-level

A modal attaches window keydown and resize listeners every time it opens. After several openings, one keypress triggers the handler multiple times. Identify the cause and show how lifecycle cleanup should work.

SecurityMid-level

A comment preview uses: preview.innerHTML = userComment; Review the risk and propose a safe implementation for plain text and for the case where a restricted subset of formatting is required.

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