Bug: Falsy thisArg (0, '', false) overridden in arrForEach/iterForOf/objForEachKey #561

[nev21]

Truthy checks (thisArg || target) incorrectly overrode legitimate falsy values such as 0, '', false, and null with the array/iterator/object being iterated, violating standard JavaScript thisArg semantics.

Replace the truthy fallback with isStrictNullOrUndefined(thisArg) so that only null and undefined trigger the default-to-target behaviour, while any other falsy value is passed through unchanged.

Also correct the arrForEach callback signature: the third parameter is ArrayLike<T>, not T[], matching the actual argument passed.

Fixes #561

Affected files:

• lib/src/array/forEach.ts
• lib/src/iterator/forOf.ts
• lib/src/object/for_each_key.ts

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.43%. Comparing base (9362b6e) to head (fa10045).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #566   +/-   ##
=======================================
  Coverage   99.43%   99.43%           
=======================================
  Files         150      150           
  Lines        4452     4460    +8     
  Branches      949      951    +2     
=======================================
+ Hits         4427     4435    +8     
  Misses         25       25           

Files with missing lines	Coverage Δ
lib/src/array/forEach.ts	100.00% <100.00%> (ø)
lib/src/iterator/forOf.ts	100.00% <100.00%> (ø)
lib/src/object/for_each_key.ts	100.00% <100.00%> (ø)

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[Copilot]

Pull request overview

This PR fixes falsy thisArg handling in core iteration helpers so 0, "", and false are passed through instead of being replaced by the iterated target.

Changes:

• Replaces truthy thisArg || target fallbacks with null/undefined checks.
• Updates arrForEach callback typing for array-like inputs.
• Adds regression tests for omitted, null/undefined, and falsy thisArg values.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
lib/src/array/forEach.ts	Updates arrForEach thisArg fallback and callback array parameter type.
lib/src/iterator/forOf.ts	Updates iterator callback thisArg fallback.
lib/src/object/for_each_key.ts	Updates object key iteration callback thisArg fallback.
lib/test/src/common/helpers/array.test.ts	Adds arrForEach regression coverage for thisArg behavior.
lib/test/src/common/iterator/forOf.test.ts	Adds iterForOf regression coverage for thisArg behavior.
lib/test/src/common/object/for_each_key.test.ts	Adds objForEachKey regression coverage for thisArg behavior.

Comments suppressed due to low confidence (2)

lib/src/array/forEach.ts:59

• This evaluates the null/undefined fallback on every element even though thisArg and theArray are loop-invariant. arrForEach is a hot utility used throughout the package, so computing the effective callback this once before the loop would avoid an extra helper call per item.

                if (callbackfn[CALL](isStrictNullOrUndefined(thisArg) ? theArray as any : thisArg, theArray[idx], idx, theArray) === -1) {

lib/src/object/for_each_key.ts:45

• The effective callback this value is recomputed for every property even though it does not change during iteration. Computing it once before the for...in loop would avoid an extra helper call per own property.

                if (callbackfn[CALL](isStrictNullOrUndefined(thisArg) ? theObject : thisArg, prop, theObject[prop as keyof T]) === -1) {

[Copilot]

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[nevware21-bot]

Approved by nevware21-bot