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Diff two flat objects

intermediate JSON Challenge 6 of 18

Write diffObjects(before, after) for two flat objects, such as an expected and an actual API response. It returns { added, removed, changed }.

Requirements

added: keys that exist only in after, with their values.
removed: keys that exist only in before, with their values.
changed: keys in both whose values differ, as { from, to }.
Decide presence by whether the key exists, not by whether the value is undefined.
Compare values with Object.is semantics, so 1 and '1' differ and NaN equals NaN.
Do not mutate either input.

Expected output

diffObjects({ a: 1, b: 2 }, { b: 3, c: 4 }) → { added: { c: 4 }, removed: { a: 1 }, changed: { b: { from: 2, to: 3 } } }

Test cases (6)

○reports added, removed and changed keys
○identical objects produce an empty diff
○a key present with value undefined is not missing
○type changes count as changes
○NaN compared with NaN is unchanged
○does not mutate the inputs

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Results

Run the tests to see results here.