javascriptEASYOUTPUT PREDICTION
Warm up with nested array transform
Easy JavaScript arena: map, filter, reduce, grouping, and immutable updates
XP reward
100
Coins
8
Target time
18m
Analytics events need to be grouped into a compact dashboard model. You are working inside a modern JavaScript application, and the arena only clears when the result is safe, deterministic, and explainable.
Learning objective
Learn to apply map, filter, reduce, grouping, and immutable updates in a modern JavaScript application while explaining the invariant, safety constraints, and hidden edge cases.
Mission order
Events contain user, category, value, and timestamp fields. Implement the direct solution first, then document the one edge case that can break it. Submit the solution plus enough reasoning to pass hidden edge cases.Visible checks
selects the safest option
Expected: B
includes justification
Expected: mentions correctness or risk
Clear requirements
- Demonstrates map, filter, reduce, grouping, and immutable updates
- Handles the visible sample and hidden edge cases
- Keeps output deterministic and explainable
- Avoids unsafe dynamic execution
Secure validation contract
Judge type
OUTPUT PREDICTION
Complexity target
Correct option plus risk-aware explanation
Workspace
Reasoning panel
Test Results
Run the visible checks when your first pass is ready.
Clear Protocol
1Read the scenario and restate the expected output shape.
2Run visible checks before chasing hidden edge cases.
3Use Genie for one nudge if stuck, then explain the invariant.
4Submit only when the result is deterministic and safe.
Rewards
XP
100
Coins
8
Mission Route
Hints
Hints are metered and logged for No Hint Hero runs.
Genie Mentor Core
Hint protocol / contextual guardrails active
Progressive hints
Failed-test aware
Solution guarded
Mission: javascript-easy-array-transform0 attempts0 failed tests0 hints used
Progressive hint depth
Genie: Genie online. I use your mission, attempts, failed tests, hints, and path context to coach the next rep without dumping answers first.