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Updated: 2026年5月31日
Arrow Function
Original task (JA): アロー関数
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Conclusion
Arrow Function — free browser-based JavaScript practice
Why it matters in real projects
アロー関数は (引数) => 戻り値 の形式です。 Similar patterns appear daily in code review and production UI work.Step-by-step workflow
1. Read the guide and understand the goal of "Arrow Function" 2. Review the JavaScript editor pane and start from the starter code 3. Open hints if stuck; compare your diff with the sample solution 4. Click Run and inspect preview/console output 5. Auto-check looks for output containing: 10. 6. After success, continue with adjacent exercises in the same categoryCore concept explained
アロー関数は (引数) => 戻り値 の形式です。Technical focus
Key JavaScript APIs: console.log.Hint before you peek at the solution
const double = (x) => x * 2;Sample solution walkthrough
JavaScript APIs used: console.log. Verify spelling and async/await usage. Explanation: アロー関数は (引数) => 戻り値 の形式です。 Hint recap: const double = (x) => x * 2;Solution code
📝 Sample code
const double = (x) => x * 2;
console.log(double(5));Common mistakes for this exact task
・Skipping the hint: const double = (x) => x * 2;Troubleshooting
Q: Preview does not change after Run A: Ensure you edited the JavaScript pane and clicked Run. Q: Looks correct but check fails A: Auto-check looks for output containing: 10. Look for typos, full-width spaces, or unclosed tags. Q: Console shows errors A: Open DevTools Console and fix bracket/quote mismatches at the reported line. Q: Hard to type on mobile A: Use landscape mode or continue on desktop—the same URL keeps progress in localStorage.Interview / portfolio tips
・Explain the techniques in "Arrow Function" in your own words within 30 seconds ・Practice walking through each line of the sample solution on a whiteboard ・Connect this task to a real component you would ship ・Mention responsive or accessibility trade-offs ・Describe when you use: console.logWhat to do after you pass
Move to the next exercise in the js-basic track, then continue the learning roadmap at /en/learning/js-basic/.Keywords
Free hands-on exercise covering アロー関数, js-basic, 初級, console.log, arrow function—search-friendly guide for Arrow Function.🧪 Try it here — safe to break things
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Jump to editor■ Exercise task
doubleというアロー関数を定義し、引数を2倍して返してください。5を渡して10が出力されること。
Hint if stuck
const double = (x) => x * 2;