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Remove Duplicates

By FrontendAtlas Team · Updated Jan 31, 2026

Implement uniqueArray(arr) that removes duplicates while preserving order. Use a Set for O(n) time and clarify how to treat objects by reference, NaN, and mixed types so behavior is explicit and predictable. Concepts: arrays, sets, deduplication, iteration.

What you’ll build / What this tests

This premium javascript coding focuses on Remove Duplicates. You’ll apply arrays and sets thinking with easy level constraints. The prompt emphasizes Implement uniqueArray(arr) that removes duplicates while preserving order. Use a Set for O(n) time and clarify….

Learning goals

Translate the prompt into a clear javascript API signature and return shape.
Apply arrays, sets, deduplication techniques to implement remove duplicates.
Handle easy edge cases without sacrificing readability.
Reason about time/space complexity and trade-offs in javascript.

Key decisions to discuss

Define the exact input/output contract before coding.
Choose iteration vs higher-order methods for readability.
Prioritize predictable edge-case handling over micro-optimizations.

Evaluation rubric

Correctness: covers required behaviors and edge cases.
Clarity: readable structure and predictable control flow.
Complexity: avoids unnecessary work for large inputs.
API discipline: no mutation of inputs; returns expected shape.
Testability: solution is easy to unit test.

Constraints / Requirements

Preserve input order and handle empty arrays safely.
Avoid prototype pitfalls when reading object keys.
Do not mutate input arrays; preserve item order.
Handle empty or missing inputs without throwing errors.
Keep runtime close to linear time where possible.
Prefer a pure function: no side effects beyond the return value.

Mini snippet (usage only)

// Example usage
const arr = /* remove duplicates input */;
const result = unique(arr);
console.log(result);

// Edge case check
const empty = arr ?? null;
const fallback = unique(arr);
console.log(fallback);

// Expected: describe output shape, not the implementation
// (no solution code in preview)

Common pitfalls

Mutating inputs instead of returning a new value.
Skipping edge cases like empty input, duplicates, or nulls.
Overlooking time complexity for large inputs.