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EasyPythonJavaScriptTypeScript

Implement promisify()

BackendAsync

Node.js core uses error-first callbacks: (err, result) => void.
Implement promisify(fn) that wraps such a function to return a Promise.

promisify(fn)(...args) should:

  • Resolve with result if the callback is called with (null, result).
  • Reject with the error if the callback is called with (err).

solve drives your implementation through a series of test cases
and returns whether each resolved or rejected.

Sample tests

Test #1Resolve with value
Input: [[{"fail":false,"value":42}]]
Output: [{"ok":true,"val":42}]
Test #2Reject on error
Input: [[{"fail":true,"value":null}]]
Output: [{"ok":false}]
Test #3Mixed resolve and reject
Input: [[{"fail":false,"value":"hello"},{"fail":true,"value":null}]]
Output: [{"ok":true,"val":"hello"},{"ok":false}]
Test #4Falsy value (0) still resolves
Input: [[{"fail":false,"value":0}]]
Output: [{"ok":true,"val":0}]
Test #5Boolean values
Input: [[{"fail":false,"value":true},{"fail":false,"value":false}]]
Output: [{"ok":true,"val":true},{"ok":true,"val":false}]
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