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MediumDSAAsked in 20246 min read

Object Difference

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The problem

Problem, as an interviewer would state it: "Implement objectDiff(a, b) — returning a description of how object b differs from object a: which paths were added, which were removed, and which changed (with the old and new value), recursing into nested objects."

Examples:

Code
objectDiff({ a: 1, b: { c: 2 } }, { a: 1, b: { c: 3 }, d: 4 });
// added: { d: 4 }, removed: {}, changed: { "b.c": { from: 2, to: 3 } }

Clarifying questions expected:

  • What output shape is wanted — flat dot-paths, or a nested structure mirroring the input?
  • How should arrays be compared, and how should NaN, +0 and -0 be treated?
  • Must a key that exists with the value undefined be distinguished from a missing key?

Code / implementation expected: Yes — real, direct proof of each category, of nested paths, and of the equality edge cases.

  • object

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Solution

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6 min read · 9 sections

Run the code

Edit the code and run it here. Each console line with an expected value becomes a test.

JavaScriptReal, direct proof: a deep diff reports added, removed and changed paths, with Object.is semantics for NaN and signed zero
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