What is the time and space complexity of Implement promisify()?

Time complexity: O(1). Space complexity: O(1).

Implement promisify()

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Solution Guide: Implement promisify()

Approach

Return a new function that wraps the original callback-based function in a Promise. Pass all user arguments plus a final callback to the original function. In the callback, reject on error or resolve with the result, following the Node.js (err, result) convention.

Complexity Analysis

Time: O(1)
Space: O(1)

Pattern

Promisify Pattern

Why It Works

The adapter appends an error-first callback that bridges the callback world to the Promise world, enabling async/await usage with legacy Node.js-style APIs.

Updated Feb 2026