Implement Array.prototype.map

What you’ll build / What this tests

This premium javascript coding focuses on Implement Array.prototype.map. You’ll apply arrays and callbacks thinking with easy level constraints. The prompt emphasizes Recreate the native .map() method without using it. Your myMap must call callbackFn(value, index, array) for….

Learning goals

• Translate the prompt into a clear javascript API signature and return shape.
• Apply arrays, callbacks, iteration techniques to implement implement array.prototype.map.
• 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 callbackFn = /* implement array.prototype.map input */;
const thisArg = /* config */;
const result = solve(callbackFn, thisArg);
console.log(result);

// Edge case check
const empty = callbackFn && thisArg ?? null;
const fallback = solve(callbackFn, thisArg);
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.

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