fix(isDeepKey): improve deep key detection to match strict patterns

[ramong26]

What

• Improved the isDeepKeyfunction to strictly detect only valid deep key patterns.
• Now returns false for invalid patterns such as 'a.', '.a', 'a[b', 'a]b]', and 'a][b]'.
• Returns true only for keys that match valid deep key patterns (e.g., 'a.b', 'a[b]', 'a.b.c', 'a[b][c]').
• Ensured isKeyuses the same consistent deep property regex for property path detection.

Why

• The previous implementation returned true for some invalid patterns, which could lead to incorrect behavior.
• This change ensures that only syntactically valid deep keys are detected, matching the documented examples and improving reliability.

Test

• Added and updated unit tests in isDeepKey.spec.ts to cover both valid and invalid deep key patterns.
• Verified that isKey and isDeepKeyare consistent in their detection logic.

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Project	Deployment	Actions	Updated (UTC)
es-toolkit	Error		Feb 17, 2026 10:49am

[Copilot]

Pull request overview

This PR tightens deep-key detection in the compat layer so functions like get/has/unset only treat syntactically valid deep-path strings as deep keys (and otherwise treat the string as a literal property key).

Changes:

• Refines isDeepKey to reject several previously-accepted invalid patterns.
• Expands isDeepKey unit tests to cover additional valid/invalid inputs.
• Adds a null-guard in findIndex’s object-shorthand handling.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/compat/array/findIndex.ts	Adds explicit handling for doesMatch === null in the object-shorthand branch.
src/compat/_internal/isDeepKey.ts	Reworks deep-key detection logic for dot/bracket patterns.
src/compat/_internal/isDeepKey.spec.ts	Adds tests for additional invalid patterns and a few more valid cases.

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[Copilot]

The updated tests cover a handful of invalid patterns, but they don't cover several false positives the new implementation still allows (e.g. a..b, a.b., a[b][c, a[b]], a[b]c, a.b[). Adding cases like these would prevent regressions and ensure the “strict pattern” behavior described in the PR.

Suggested change

	expect(isDeepKey('a][b')).toBe(false);
	expect(isDeepKey('a][b')).toBe(false);
	expect(isDeepKey('a..b')).toBe(false);
	expect(isDeepKey('a.b.')).toBe(false);
	expect(isDeepKey('a[b][c')).toBe(false);
	expect(isDeepKey('a[b]]')).toBe(false);
	expect(isDeepKey('a[b]c')).toBe(false);
	expect(isDeepKey('a.b[')).toBe(false);

[Copilot]

The dot check only looks at the first '.' and only enforces it isn't the first/last character. This still returns true for syntactically invalid dot paths like a..b (empty segment) or a.b. (trailing dot), which contradicts the PR goal of accepting only strict deep-key patterns. Consider validating the full string (e.g., reject consecutive dots / any empty segment) rather than just indexOf('.') bounds checks.

Suggested change

	if (dotIndex > 0 && dotIndex < key.length - 1) {
	return true;
	if (dotIndex !== -1) {
	const segments = key.split('.');
	if (segments.length > 1 && segments.every(segment => segment.length > 0)) {
	return true;
	}

[Copilot]

The bracket check only verifies that the first '[' appears before the first ']'. It will still return true for invalid/mismatched bracket patterns like a[b][c (unclosed), a[b]] (extra ']'), a.b[ (unclosed), or a[b]c (missing separator). To meet the strict-pattern intent, this likely needs a small parser/regex that validates balanced bracket segments and disallows stray brackets outside of them.