Implement Array.forEach

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Solution Guide: Implement Array.forEach

Approach

Loop through the array and invoke the callback with (element, index, array) for each item. Unlike map, forEach returns undefined and is used purely for side effects. The implementation does not collect return values.

Complexity Analysis

Time
O(n)
Space
O(1)

Pattern

Array Polyfill

Why It Works

forEach provides a cleaner syntax than a for loop for executing side effects on each element. It always iterates the entire array and cannot be short-circuited with break or return.

Updated Feb 2026