Fix deepStrictEqual to perform deep value comparison #273

Copilot · 2026-02-11T17:15:12Z

Fix deepStrictEqual to perform deep value comparison

Plan:

Explore repository and understand current implementation
Fix the _deepEquals function to support deep comparison in strict mode
Update existing tests to expect deep value equality instead of reference equality
Add new test cases for the specific examples in the problem statement
Run tests to verify all changes work correctly
Request code review and run CodeQL security check
Add comprehensive tests for deepEqual with loose equality
Update documentation for v0.1.7 changes

Changes:

Original Implementation Fix

Fixed deepStrictEqual to perform deep value comparison instead of reference equality
Updated tests to verify deep value equality for strict comparison

Comprehensive Tests

Added test suite for deepStrictEqual with strict type checking
Added test suite for deepEqual with loose equality

Documentation Updates (v0.1.7)

Updated docs/migration/migrating-from-node-assert.md:

Section 3.1: Clarified behavior change in v0.1.7 (now matches Node.js)
Section 3.2: Updated comparison table to show identical behavior
Section 4.1: Marked deepStrictEqual as identical to Node.js
Sections 5.2-5.4: Updated examples to show no migration needed for v0.1.7+
Section 6.2: Updated migration strategy (import changes only)
Section 7: Updated GitHub Copilot prompts
Section 8: Updated common patterns (no changes needed)
Section 11: Updated troubleshooting for v0.1.7
Section 12: Updated best practices
Section 13: Updated migration checklist

Updated README.md:

Added "What's New in v0.1.7" section
Documented deepStrictEqual behavior change
Updated recommended version to >= 0.1.7
Added examples showing strict vs loose equality

Original prompt

We need to update the deepStrictEqual implementation to support these passing examples
* assert.deepStrictEqual({ a: 1 }, { a: 1 }); // Passes
* assert.deepStrictEqual({ a: 1 }, { a: "1" }); // Throws AssertionFailure
* assert.deepStrictEqual([1, 2], [1, 2]); // Passes
* assert.deepStrictEqual([1, 2], [2, 1]); // Throws AssertionFailure
* assert.deepStrictEqual({ a: { b: 1 } }, { a: { b: 1 } }); // Passes
* assert.deepStrictEqual({ a: { b: 1 } }, { a: { b: "1" } }); // Throws AssertionFailure
* assert.deepStrictEqual([{ a: 1 }], [{ a: 1 }]); // Passes
* assert.deepStrictEqual([{ a: 1 }], [{ a: "1" }]); // Throws AssertionFailure
otherwise we are just performing an object equality. Add tests for these cases and then update the implementation

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Co-authored-by: nev21 <82737406+nev21@users.noreply.github.com>

nev21 · 2026-02-12T01:24:15Z

@copilot Add tests for the examples in deepEqual as well make sure that comparing a: 1 with a: "1" passes

Co-authored-by: nev21 <82737406+nev21@users.noreply.github.com>

Copilot · 2026-02-12T01:28:41Z

@copilot Add tests for the examples in deepEqual as well make sure that comparing a: 1 with a: "1" passes

Added comprehensive tests for deepEqual with loose equality in commit d2d8dea. The new test suite validates that:

{ a: 1 } == { a: "1" } passes (loose type coercion)
{ a: { b: 1 } } == { a: { b: "1" } } passes (nested loose equality)
[{ a: 1 }] == [{ a: "1" }] passes (arrays with objects, loose equality)

All 2,117 tests passing ✓

Co-authored-by: nev21 <82737406+nev21@users.noreply.github.com>

nev21 · 2026-02-12T03:19:59Z

@copilot update the #file:migrating-from-node-assert.md and readme,md files with the changes to deepStrictEqual introduced in this change that will be published as v0.1.7

Copilot · 2026-02-12T03:24:09Z

@copilot update the #file:migrating-from-node-assert.md and readme,md files with the changes to deepStrictEqual introduced in this change that will be published as v0.1.7

Updated both documentation files in commit da9b07d:

migrating-from-node-assert.md:

Section 3.1: Documented v0.1.7 behavior change (now matches Node.js)
Updated all migration examples to show no changes needed for v0.1.7+
Updated migration strategy, patterns, and best practices

README.md:

Added "What's New in v0.1.7" section
Documented deepStrictEqual behavior change with examples
Updated recommended version to >= 0.1.7
Added migration note for users upgrading from older versions

Copilot

Pull request overview

This PR fixes assert.deepStrictEqual() so it performs deep value comparison for objects/arrays (with strict type checking on nested values), instead of incorrectly requiring reference equality.

Changes:

Removed an early-return in _deepEquals() that prevented deep comparison when strict: true.
Updated deepStrictEqual tests to assert deep value equality (not same-reference equality).
Added additional deepEqual (loose) tests demonstrating nested coercive comparisons.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.

File	Description
`core/test/src/assert/assert.equals.test.ts`	Expands deepEqual/deepStrictEqual test cases to validate value-based deep comparison behavior.
`core/src/assert/funcs/equal.ts`	Removes strict-mode early return so strict mode continues into deep comparison logic.
`common/config/rush/npm-shrinkwrap.json`	Updates shrinkwrap due to dependency patch bumps.

Files not reviewed (1)

common/config/rush/npm-shrinkwrap.json: Language not supported

Copilot · 2026-02-12T03:26:02Z

core/src/assert/funcs/equal.ts

        if (isEquals !== null) {
            return isEquals;
        }

-        if (options.strict === true) {
-            // If strict is set and we get here, then the values are not strictly equal
-            return false;
-        }
-
        if (isPlainObject(value) && isPlainObject(expected)) {


With the strict early-return removed, _deepEquals() can now reach the typeFn comparison path for types like Promise/function/WeakMap/etc. Several of those type comparers are currently _strictEquals, which returns null for non-primitive non-reference-equal values. Returning null from _deepEquals() breaks nested comparisons because callers check === false (e.g. in _iterEquals / _matchKeys), so null is treated as “equal” and deepStrictEqual can incorrectly pass for objects/arrays containing different Promises/functions. Ensure _deepEquals() never returns null (coerce null -> false), or wrap the _typeEquals entries that use _strictEquals to return a boolean (e.g. (_strictEquals(...) === true)).

@copilot apply changes based on this feedback

Co-authored-by: nev21 <82737406+nev21@users.noreply.github.com>

nev21

LGTM

codecov · 2026-02-12T06:36:15Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.43%. Comparing base (808339a) to head (291cb95).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #273      +/-   ##
==========================================
- Coverage   91.43%   91.43%   -0.01%     
==========================================
  Files          78       78              
  Lines        3445     3443       -2     
  Branches      887      886       -1     
==========================================
- Hits         3150     3148       -2     
  Misses        295      295

Files with missing lines	Coverage Δ
core/src/assert/funcs/equal.ts	`82.01% <ø> (-0.16%)`	⬇️

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
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nevware21-bot

Approved by nevware21-bot

…comparisons Fixes issue from PR #273 where _deepEquals() returning null from _strictEquals for non-reference-equal Promises/functions/WeakMaps caused nested comparisons to fail incorrectly. Callers check (=== false), treating null as "equal". Two bugs fixed: 1. Added _strictEqualsBool wrapper to convert null → false for types that should only be equal if reference-equal (Promise, function, symbol, WeakMap, WeakSet) 2. Fixed _getTypeComparer() objType lookup bug where undefined objType accessed _typeEquals["undefined"] returning wrong comparer instead of falling back to theType Changes: - core/src/assert/funcs/equal.ts: * Added _strictEqualsBool wrapper function * Updated _typeEquals map for promise/function/symbol/weakmap/weakset * Fixed _getTypeComparer to check (objType && _typeEquals[objType]) - core/test/src/assert/assert.equals.test.ts: * Added regression test for Promise/function in nested objects/arrays

…comparisons (#275) Fixes issue from PR #273 where _deepEquals() returning null from _strictEquals for non-reference-equal Promises/functions/WeakMaps caused nested comparisons to fail incorrectly. Callers check (=== false), treating null as "equal". Two bugs fixed: 1. Added _strictEqualsBool wrapper to convert null → false for types that should only be equal if reference-equal (Promise, function, symbol, WeakMap, WeakSet) 2. Fixed _getTypeComparer() objType lookup bug where undefined objType accessed _typeEquals["undefined"] returning wrong comparer instead of falling back to theType Changes: - core/src/assert/funcs/equal.ts: * Added _strictEqualsBool wrapper function * Updated _typeEquals map for promise/function/symbol/weakmap/weakset * Fixed _getTypeComparer to check (objType && _typeEquals[objType]) - core/test/src/assert/assert.equals.test.ts: * Added regression test for Promise/function in nested objects/arrays

Initial plan

47477ee

Copilot AI assigned Copilot and nev21 Feb 11, 2026

Copilot started work on behalf of nev21 February 11, 2026 17:15 View session

Copilot AI and others added 2 commits February 11, 2026 17:18

Initial plan for deepStrictEqual fix

c04b405

Co-authored-by: nev21 <82737406+nev21@users.noreply.github.com>

Fix deepStrictEqual to support deep value comparison

848747f

Co-authored-by: nev21 <82737406+nev21@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Update deepStrictEqual implementation to support passing examples~~ Fix deepStrictEqual to perform deep value comparison Feb 11, 2026

Copilot AI requested a review from nev21 February 11, 2026 17:32

Copilot finished work on behalf of nev21 February 11, 2026 17:32

Copilot started work on behalf of nev21 February 12, 2026 01:24 View session

Add comprehensive tests for deepEqual with loose equality

d2d8dea

Co-authored-by: nev21 <82737406+nev21@users.noreply.github.com>

Copilot finished work on behalf of nev21 February 12, 2026 01:31

Fix deepStrictEqual to perform deep value comparison

47eb64d

Co-authored-by: nev21 <82737406+nev21@users.noreply.github.com>

nev21 force-pushed the copilot/update-deepstrictequal-implementation branch from 0eb3961 to 47eb64d Compare February 12, 2026 03:17

Merge branch 'main' into copilot/update-deepstrictequal-implementation

9027bd9

Copilot started work on behalf of nev21 February 12, 2026 03:20 View session

nev21 marked this pull request as ready for review February 12, 2026 03:22

nev21 requested review from a team as code owners February 12, 2026 03:22

Copilot AI review requested due to automatic review settings February 12, 2026 03:22

Copilot started reviewing on behalf of nev21 February 12, 2026 03:22 View session

Copilot finished work on behalf of nev21 February 12, 2026 03:24

Copilot AI reviewed Feb 12, 2026

View reviewed changes

Update documentation for deepStrictEqual changes in v0.1.7

291cb95

Co-authored-by: nev21 <82737406+nev21@users.noreply.github.com>

nev21 force-pushed the copilot/update-deepstrictequal-implementation branch from da9b07d to 291cb95 Compare February 12, 2026 06:24

nev21 approved these changes Feb 12, 2026

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nev21 enabled auto-merge (squash) February 12, 2026 06:25

nev21 reviewed Feb 12, 2026

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nevware21-bot approved these changes Feb 12, 2026

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nev21 merged commit 119dd67 into main Feb 12, 2026
11 checks passed

nev21 deleted the copilot/update-deepstrictequal-implementation branch February 12, 2026 06:43

Copilot AI mentioned this pull request Feb 12, 2026

[Release] Increase version to 0.1.7 #274

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nev21 mentioned this pull request Feb 12, 2026

fix(deepEqual): prevent null return breaking nested Promise/function comparisons #275

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nev21 added this to the 0.1.7 milestone Feb 12, 2026

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Fix deepStrictEqual to perform deep value comparison #273

Fix deepStrictEqual to perform deep value comparison #273

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Fix deepStrictEqual to perform deep value comparison #273

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