fix(merge, mergeWith): Handle top-level type mismatch consistently

[Seol-JY]

Summary

Fixes #1394

merge and mergeWith now handle top-level type mismatches consistently with nested property behavior.

Before

merge(["1"], {a: 2})             // [ '1', a: 2 ]
merge({x: ["1"]}, {x: {a: 2}}).x // { a: 2 }
// Inconsistent behavior

After

merge(["1"], {a: 2})             // { a: 2 }
merge({x: ["1"]}, {x: {a: 2}}).x // { a: 2 }
// Consistent behavior - source type wins

Changes

• Added top-level type checking in merge and mergeWith to match nested property logic from
  PR fix(merge): Handle edge-case for merge #556
• Added test cases for top-level type mismatch scenarios

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Project	Deployment	Preview	Comments	Updated (UTC)
es-toolkit	Ready	Preview	Comment	Nov 21, 2025 6:52pm

[Copilot]

Pull request overview

This PR fixes inconsistent behavior in merge and mergeWith functions when handling type mismatches between target and source arguments. Previously, top-level type mismatches (e.g., array target with object source) behaved differently than nested property type mismatches. The fix ensures that in both cases, the source type takes precedence.

Key changes:

• Added top-level type checking in both merge and mergeWith to detect array/object mismatches before iteration
• When types mismatch, creates a fresh target of the source's type and recursively merges
• Added test cases demonstrating the consistent behavior between top-level and nested type mismatches

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/object/merge.ts	Added top-level type mismatch detection (lines 48-56) that creates fresh target when types don't match
src/object/mergeWith.ts	Added identical top-level type mismatch detection (lines 57-65) consistent with merge.ts
src/object/merge.spec.ts	Added test verifying top-level type mismatch behavior matches nested behavior
src/object/mergeWith.spec.ts	Added test verifying top-level type mismatch behavior matches nested behavior for mergeWith

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