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assert: fix _deepEqual and improve assert.md #11128

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@joyeecheung joyeecheung commented Feb 2, 2017

This is the more semver-patch part of #10282.

Fix _deepEqual

Refactors _deepEqual and fixes a few code paths that lead to
behaviors contradicting what the doc says. Before this commit
certain types of objects (Buffers, Dates, etc.) are not checked
properly, and can get away with different prototypes AND different
enumerable owned properties because _deepEqual would jump to
premature conclusion for them.

Since we no longer follow CommonJS unit testing spec,
the checks for primitives and object prototypes are moved
forward for faster failure.

Improve regexp and float* array checks:

  • Don't compare lastIndex of regexps, because they are not
    enumerable, so according to the docs they should not be compared
  • Compare flags of regexps instead of separate properties
  • Use built-in tags to test for float* arrays instead of using
    instanceof

Refs: #10282 (comment)
Refs: #10258 (comment)

Improve documentation

Use the term "Abstract Equality Comparison" and "Strict Equality
Comparison" from ECMAScript specification to refer to the operations
done by == and ===, instead of the informal
"equal comparison operator" and "strict equality operator".

Clarify that deep strict comparisons checks [[Prototype]]
property, instead of the vague "object prototypes".

Suggest using Object.is() to avoid the caveats of +0, -0 and NaN.

Add a MDN link explaining what enumerable "own" properties are.

Checklist
  • make -j4 test (UNIX), or vcbuild test (Windows) passes
  • tests and/or benchmarks are included
  • documentation is changed or added
  • commit message follows commit guidelines
Affected core subsystem(s)

test, assert, doc

@nodejs-github-bot nodejs-github-bot added the assert Issues and PRs related to the assert subsystem. label Feb 2, 2017
@joyeecheung joyeecheung changed the title assert: refactor assert and improve assert.md assert: refactor _deepEqual and improve assert.md Feb 2, 2017
@joyeecheung joyeecheung changed the title assert: refactor _deepEqual and improve assert.md assert: fix _deepEqual and improve assert.md Feb 2, 2017
@joyeecheung joyeecheung added doc Issues and PRs related to the documentations. test Issues and PRs related to the tests. labels Feb 2, 2017
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joyeecheung commented Feb 2, 2017

@mscdex mscdex removed doc Issues and PRs related to the documentations. test Issues and PRs related to the tests. labels Feb 2, 2017
@jasnell jasnell added the semver-major PRs that contain breaking changes and should be released in the next major version. label Feb 2, 2017
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Benchmarks results (benchmarks taken from #11092). Note that this implementation favors fast failures, though failures are not benchmarked(when an assertion fails the process should probably be terminated anyway).

see results
                                                                                                  improvement confidence      p.value
 assert/deepequal-buffer.js method="nonstrict" len=100 n=1000                                        -92.69 %        *** 1.398352e-10
 assert/deepequal-buffer.js method="strict" len=100 n=1000                                           -87.27 %        *** 8.988908e-07
 assert/deepequal-prims-and-objs-big-array.js method="nonstrict" len=100000 n=25 prim="array"          0.52 %            5.671380e-01
 assert/deepequal-prims-and-objs-big-array.js method="nonstrict" len=100000 n=25 prim="boolean"        1.33 %            3.162478e-01
 assert/deepequal-prims-and-objs-big-array.js method="nonstrict" len=100000 n=25 prim="new-array"      1.39 %          * 2.256608e-02
 assert/deepequal-prims-and-objs-big-array.js method="nonstrict" len=100000 n=25 prim="null"           1.12 %            1.546353e-01
 assert/deepequal-prims-and-objs-big-array.js method="nonstrict" len=100000 n=25 prim="number"        -0.52 %            7.352546e-01
 assert/deepequal-prims-and-objs-big-array.js method="nonstrict" len=100000 n=25 prim="object"        -0.53 %            5.363293e-01
 assert/deepequal-prims-and-objs-big-array.js method="nonstrict" len=100000 n=25 prim="string"         0.48 %            5.514581e-01
 assert/deepequal-prims-and-objs-big-array.js method="nonstrict" len=100000 n=25 prim="undefined"      0.70 %            2.601707e-01
 assert/deepequal-prims-and-objs-big-array.js method="strict" len=100000 n=25 prim="array"             0.59 %            4.341103e-01
 assert/deepequal-prims-and-objs-big-array.js method="strict" len=100000 n=25 prim="boolean"           1.73 %         ** 9.211000e-03
 assert/deepequal-prims-and-objs-big-array.js method="strict" len=100000 n=25 prim="new-array"         1.30 %            1.185455e-01
 assert/deepequal-prims-and-objs-big-array.js method="strict" len=100000 n=25 prim="null"              0.68 %            3.269869e-01
 assert/deepequal-prims-and-objs-big-array.js method="strict" len=100000 n=25 prim="number"           -2.51 %            5.382094e-02
 assert/deepequal-prims-and-objs-big-array.js method="strict" len=100000 n=25 prim="object"            2.23 %            8.626440e-02
 assert/deepequal-prims-and-objs-big-array.js method="strict" len=100000 n=25 prim="string"            0.20 %            7.698036e-01
 assert/deepequal-prims-and-objs-big-array.js method="strict" len=100000 n=25 prim="undefined"         0.86 %            3.789055e-01
 assert/deepequal-prims-and-objs-big-loop.js method="nonstrict" n=1000000 prim="array"                 6.32 %        *** 4.516185e-04
 assert/deepequal-prims-and-objs-big-loop.js method="nonstrict" n=1000000 prim="boolean"               9.25 %        *** 8.115494e-05
 assert/deepequal-prims-and-objs-big-loop.js method="nonstrict" n=1000000 prim="new-array"             9.36 %        *** 7.678773e-05
 assert/deepequal-prims-and-objs-big-loop.js method="nonstrict" n=1000000 prim="null"                  9.41 %        *** 2.294144e-04
 assert/deepequal-prims-and-objs-big-loop.js method="nonstrict" n=1000000 prim="number"                5.07 %          * 3.376728e-02
 assert/deepequal-prims-and-objs-big-loop.js method="nonstrict" n=1000000 prim="object"                4.23 %            1.091126e-01
 assert/deepequal-prims-and-objs-big-loop.js method="nonstrict" n=1000000 prim="string"                6.42 %        *** 5.440464e-04
 assert/deepequal-prims-and-objs-big-loop.js method="nonstrict" n=1000000 prim="undefined"             8.15 %         ** 4.303777e-03
 assert/deepequal-prims-and-objs-big-loop.js method="strict" n=1000000 prim="array"                    6.60 %          * 1.017124e-02
 assert/deepequal-prims-and-objs-big-loop.js method="strict" n=1000000 prim="boolean"                  8.82 %        *** 6.257818e-05
 assert/deepequal-prims-and-objs-big-loop.js method="strict" n=1000000 prim="new-array"               11.13 %        *** 6.845735e-04
 assert/deepequal-prims-and-objs-big-loop.js method="strict" n=1000000 prim="null"                     8.88 %        *** 1.083174e-04
 assert/deepequal-prims-and-objs-big-loop.js method="strict" n=1000000 prim="number"                   4.29 %            2.310841e-01
 assert/deepequal-prims-and-objs-big-loop.js method="strict" n=1000000 prim="object"                   7.70 %        *** 2.296652e-04
 assert/deepequal-prims-and-objs-big-loop.js method="strict" n=1000000 prim="string"                   9.81 %        *** 1.067824e-06
 assert/deepequal-prims-and-objs-big-loop.js method="strict" n=1000000 prim="undefined"               13.05 %        *** 1.293929e-05
 assert/deepequal-typedarrays.js len=1000000 method="nonstrict" n=1 type="Float32Array"                0.45 %            6.665986e-01
 assert/deepequal-typedarrays.js len=1000000 method="nonstrict" n=1 type="Float64Array"                1.62 %            1.182916e-01
 assert/deepequal-typedarrays.js len=1000000 method="nonstrict" n=1 type="Int16Array"                -98.85 %        *** 6.838162e-11
 assert/deepequal-typedarrays.js len=1000000 method="nonstrict" n=1 type="Int32Array"                -98.02 %        *** 1.541802e-11
 assert/deepequal-typedarrays.js len=1000000 method="nonstrict" n=1 type="Int8Array"                 -99.33 %        *** 1.169792e-12
 assert/deepequal-typedarrays.js len=1000000 method="nonstrict" n=1 type="Uint16Array"               -98.88 %        *** 1.836848e-11
 assert/deepequal-typedarrays.js len=1000000 method="nonstrict" n=1 type="Uint32Array"               -97.99 %        *** 7.248263e-13
 assert/deepequal-typedarrays.js len=1000000 method="nonstrict" n=1 type="Uint8Array"                -99.32 %        *** 3.145163e-11
 assert/deepequal-typedarrays.js len=1000000 method="nonstrict" n=1 type="Uint8ClampedArray"         -99.30 %        *** 5.984442e-12
 assert/deepequal-typedarrays.js len=1000000 method="strict" n=1 type="Float32Array"                   0.78 %            4.221460e-01
 assert/deepequal-typedarrays.js len=1000000 method="strict" n=1 type="Float64Array"                  -0.08 %            9.232714e-01
 assert/deepequal-typedarrays.js len=1000000 method="strict" n=1 type="Int16Array"                    -6.42 %            7.496064e-02
 assert/deepequal-typedarrays.js len=1000000 method="strict" n=1 type="Int32Array"                    -0.20 %            9.728131e-01
 assert/deepequal-typedarrays.js len=1000000 method="strict" n=1 type="Int8Array"                     -5.38 %            5.518969e-01
 assert/deepequal-typedarrays.js len=1000000 method="strict" n=1 type="Uint16Array"                   -6.58 %            2.480984e-01
 assert/deepequal-typedarrays.js len=1000000 method="strict" n=1 type="Uint32Array"                   -4.62 %            1.772045e-01
 assert/deepequal-typedarrays.js len=1000000 method="strict" n=1 type="Uint8Array"                   -10.72 %        *** 1.283864e-04
 assert/deepequal-typedarrays.js len=1000000 method="strict" n=1 type="Uint8ClampedArray"             -0.45 %            8.987984e-01

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Hmm, canary died but I can't be sure if the failures are related(most are in network-related modules, and node-sass has an error about platform support). @MylesBorins Am I using it properly?


Only [enumerable "own" properties](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties)
are considered. The `deepEqual()` implementation does not test the
[`[[Prototype]]`](https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots)
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Please move the link ref to the end of the file and use an inline ref like:

[`[[Prototype]]`][]

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I used this but seems GitHub has a little bit trouble with that(I am guessing it's the [[ and ]] somehow confuses its parser?), not sure if the tooling can deal with it?

Only [enumerable "own" properties](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties)
are considered. The `deepEqual()` implementation does not test the
[`[[Prototype]]`](https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots)
of objects, attached symbols, or non-enumerable
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This line is rather short, can you update this so that the line length is closer to 80


For the following cases, consider using ES2015 [`Object.is()`][],
which uses the
[SameValueZero](https://tc39.github.io/ecma262/#sec-samevaluezero) comparison.
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Please move this to a reference at the bottom of the file also. :-)

result += str.replace(/[\\^$.*+?()[\]{}|=!<>:-]/g, '\\$&');
result += literals[i + 1];
}
return new RegExp('^AssertionError: ' + result + '$');
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return new RegExp(`^AssertionError: ${result}$`);

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@jasnell Thanks, PTAL. I am not quite sure about what to do the [[Prototype]] part, because neither the markdown rendering of GitHub nor our tooling can deal with them:

screen shot 2017-02-04 at 2 29 21 am

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jasnell commented Feb 3, 2017

Escape the [ with a \ like so:

[\[\[Prototype\]\]][]

[\[\[Prototype\]\]]: https://example.org/link/to/whatever

For instance: [[Prototype]]

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Hmm...putting it inside ` still doesn't work:

[`\[\[Prototype\]\]`]: https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots

screen shot 2017-02-04 at 4 00 59 pm

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joyeecheung commented Feb 6, 2017

@addaleax @Trott Can you take a look at this if you have time since you've LTGM'ed #10282? Thanks!

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Same comments as on #10282 - it'd be great to cache everything at module level rather than trusting user-provided objects, or user code, not to have broken something.

lib/assert.js Outdated
}

function isArguments(tag) {
return tag == '[object Arguments]';
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===

lib/assert.js Outdated
// for a list of tags pre-defined in the spec.
// There are some unspecified tags in the wild too (e.g. typed array tags).
// Since tags can be altered, they only serve fast failures
const actualTag = Object.prototype.toString.call(actual);
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Same comment as I made in #10282 - Object.prototype.toString should be cached at module level.

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(I think the discussion about @ljharb 's comments can be moved here since those commented code is intended to be merged by this PR)

I am +1-ish on caching Object.prototype.toString and Object.keys for robustness, but I think this should be better pursued in a separate PR because this practice should be consistent across different lib modules, especially in util.objectToString(just discovered it), unless we have to avoid it for other reasons e.g. performance hit.

In the meantime I'll change Object.prototype.toString.call in this PR to use util.objectToString instead.

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Rebased and, ah...right, I was being silly, the [[Prototype]] link can be easily fixed by using named reference links :P @jasnell PTAL.

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Pinging @jasnell @Trott @addaleax for more reviews, thanks!

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Code looks good but doc needs a few tweaks.

Primitive values are compared with the [Abstract Equality Comparison][]
( `==` ).

Only [enumerable "own" properties](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties)
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Please move the link to the bottom and use an inline reference like [enumerable "own" properties][] to avoid having the over-long line

[`[[Prototype]]`][prototype-spec] of objects, attached symbols, or
non-enumerable properties (for those checks, consider using
[`assert.deepStrictEqual()`][] instead). This can lead to some
potentially surprising results. For example, the following example does no
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s/does no/does not (end of the line)


For the following cases, consider using ES2015 [`Object.is()`][],
which uses the
[SameValueZero][] comparison.
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Move this up to the previous line :-)

```

For more information, see
[MDN's guide on equality comparisons and sameness](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness).
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Even tho this is at the end of the file, please move the link to the index at the end and use an inline reference for this as well, just for consistency :-)

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One minor doc nit, but otherwise LGTM if CI is green and a CITGM run doesn't reveal anything alarming.

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Punctuation fixed, thanks! @Trott

CI: https://ci.nodejs.org/job/node-test-pull-request/6473/

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Recent CITGM jobs are all red, launched https://ci.nodejs.org/job/citgm-smoker/582/ against master and https://ci.nodejs.org/job/citgm-smoker/583/ against this PR for comparison.

because the properties on the [`Error`][] object are non-enumerable:
Only [enumerable "own" properties][] are considered. The `deepEqual()`
implementation does not test the [`[[Prototype]]`][prototype-spec] of
objects, attached symbols, or non-enumerable properties. (For those checks,
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Just spotted this... can you actually remove the parens in this sentence. It can be reworded slightly as:

Only [enumerable "own" properties][] are considered. The `deepEqual()`
implementation does not test the [`[[Prototype]]`][prototype-spec] of objects,
attached symbols, or non-enumerable properties — for such checks, consider
using [assert.deepStrictEqual()][] instead.

Also, using deepEqual() in one sentence and assert.deepStrictEqual() in another is a bit inconsistent. Consider either using the assert. in both or omitting it from both.

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Oh yes, I was thinking parens look a bit awkward too, the hyphen does the trick!
I'll use assert.deepEqual() because it has a link already. Thanks!

[Abstract Equality Comparison]: https://tc39.github.io/ecma262/#sec-abstract-equality-comparison
[Strict Equality Comparison]: https://tc39.github.io/ecma262/#sec-strict-equality-comparison
[`Object.is()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
[SameValueZero]: https://tc39.github.io/ecma262/#sec-SameValueZero
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nit: #sec-samevaluezero

For more information, see
[MDN's guide on equality comparisons and sameness][mdn-equality-guide].

[Locked]: documentation.html#documentation_stability_index
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this link is unused

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@targos Thanks for the review, updated.

New CI: https://ci.nodejs.org/job/node-test-pull-request/6492/

The CITGM for the last code change has the same amount of failure as master ( (27 failures / ±0)), not sure if we can rely on this though...

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Hmm..don't know what else does this PR need to land? CITGM is 27 failures and ±0 compared to its master.

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@joyeecheung I don’t think there’s anything speaking against landing it. :)

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@addaleax Alright, gonna land this tomorrow :) Thanks

@Trott Trott mentioned this pull request Feb 25, 2017
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Trott commented Feb 25, 2017

FYI, needs a rebase thanks to a PR I just landed.

lib/assert.js Outdated

function objEquiv(a, b, strict, actualVisitedObjects) {
if (a === null || a === undefined || b === null || b === undefined)
// GH-7178. Ensure reflexivity of deepEqual with `arguments` objects.
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This is probably a good time to change that GH reference to a full URL. Generally a good idea, but especially here since it's not in this repository, but in the archive one instead:

nodejs/node-v0.x-archive#7178

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Yep, I'll update those links, thanks!

new Int32Array([1]), // Int32Array
new Uint32Array([1]), // Uint32Array
Buffer.from([1]),
// Arguments {'0': '1'} is not here, see GH-7178
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Same here, full URL would be helpful: nodejs/node-v0.x-archive#7178

Refactors _deepEqual and fixes a few code paths that lead to
behaviors contradicting what the doc says. Before this commit
certain types of objects (Buffers, Dates, etc.) are not checked
properly, and can get away with different prototypes AND different
enumerable owned properties because _deepEqual would jump to
premature conclusion for them.

Since we no longer follow CommonJS unit testing spec,
the checks for primitives and object prototypes are moved
forward for faster failure.

Improve regexp and float* array checks:

* Don't compare lastIndex of regexps, because they are not
  enumerable, so according to the docs they should not be compared
* Compare flags of regexps instead of separate properties
* Use built-in tags to test for float* arrays instead of using
  instanceof

Use full link to the archived GitHub repository.

Use util.objectToString for future improvements to that function
that makes sure the call won't be tampered with.

Refs: nodejs#10282 (comment)
Refs: nodejs#10258 (comment)
Use the term "Abstract Equality Comparison" and "Strict Equality
Comparison" from ECMAScript specification to refer to the operations
done by `==` and `===`, instead of "equal comparison operator" and
"strict equality operator".

Clarify that deep strict comparisons checks `[[Prototype]]`
property, instead of the vague "object prototypes".

Suggest using `Object.is()` to avoid the caveats of +0, -0 and NaN.

Add a MDN link explaining what enumerable "own" properties are.
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Rebased and squashed with full github links added.

New CI: https://ci.nodejs.org/job/node-test-pull-request/6583/
CITGM against master: https://ci.nodejs.org/view/Node.js-citgm/job/citgm-smoker/599/
CITGM against this PR: https://ci.nodejs.org/view/Node.js-citgm/job/citgm-smoker/600/

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gibfahn commented Feb 25, 2017

@nodejs/citgm do these failures look reasonable?

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This is weird, the CITGM against this PR is (18 failures / -11), less failures than the master...is it just flakiness?

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Not sure why CITGM got less errors with this PR, but according previous results I am pretty sure it's not related to the code change here. I am going to land this tomorrow if no more concerns arise...

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jasnell commented Feb 27, 2017

CITGM and CI look fine. I've seen flakiness like that before.

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Landed in 562cf5a and 3d8379a, thanks!

joyeecheung added a commit that referenced this pull request Feb 27, 2017
Refactors _deepEqual and fixes a few code paths that lead to
behaviors contradicting what the doc says. Before this commit
certain types of objects (Buffers, Dates, etc.) are not checked
properly, and can get away with different prototypes AND different
enumerable owned properties because _deepEqual would jump to
premature conclusion for them.

Since we no longer follow CommonJS unit testing spec,
the checks for primitives and object prototypes are moved
forward for faster failure.

Improve regexp and float* array checks:

* Don't compare lastIndex of regexps, because they are not
  enumerable, so according to the docs they should not be compared
* Compare flags of regexps instead of separate properties
* Use built-in tags to test for float* arrays instead of using
  instanceof

Use full link to the archived GitHub repository.

Use util.objectToString for future improvements to that function
that makes sure the call won't be tampered with.

PR-URL: #11128
Refs: #10282 (comment)
Refs: #10258 (comment)
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
joyeecheung added a commit that referenced this pull request Feb 27, 2017
Use the term "Abstract Equality Comparison" and "Strict Equality
Comparison" from ECMAScript specification to refer to the operations
done by `==` and `===`, instead of "equal comparison operator" and
"strict equality operator".

Clarify that deep strict comparisons checks `[[Prototype]]`
property, instead of the vague "object prototypes".

Suggest using `Object.is()` to avoid the caveats of +0, -0 and NaN.

Add a MDN link explaining what enumerable "own" properties are.

PR-URL: #11128
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
@jasnell jasnell mentioned this pull request Apr 4, 2017
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assert Issues and PRs related to the assert subsystem. semver-major PRs that contain breaking changes and should be released in the next major version.
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