What is the time and space complexity of Implement Object.assign()?

Time complexity: O(n) where n is the total number of properties across sources. Space complexity: O(1) beyond the target object.

Implement Object.assign()

Easy

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Solution Guide: Implement Object.assign()

Approach

Iterate over each source object, copying its own enumerable string-keyed properties to the target using Object.keys, and its enumerable symbol-keyed properties using Object.getOwnPropertySymbols. Skip null/undefined sources and throw on null/undefined target.

Complexity Analysis

Time: O(n) where n is the total number of properties across sources
Space: O(1) beyond the target object

Pattern

Shallow Copy

Why It Works

Copying only own enumerable properties with Object.keys matches the native Object.assign specification, and later sources naturally overwrite earlier ones for the same key.

Updated Feb 2026