Refactor “Loose equality using ==” #4133

sideshowbarker · 2021-04-15T14:16:38Z

This change refactors the entire “Loose equality using ==” section in the “Equality comparisons and sameness” article — with the goal of improving its usability, and at the same time fixing some technical problems with it.

Split the giant loose-equality table into a series of individual tables
Use &nsbp; in comparison formulas, to prevent bad/ugly breaks that otherwise occur in the tables.
Remove all the style attributes from the loose-equality tables (they are unnecessary, and we’d not be able to have styles in it when we move the table source to being markdown).
Make it explicit that the comparisons are to the number, bigint, and string primitives — not their corresponding objects. (Otherwise, especially because it has Number, BigInt, String, and Boolean in titlecase, it looked like it was about the objects, not the primitives).
Remove unnecessary redundancy/over-emphasis about comparisons to undefined and null: It’s simple:
undefined == null is true, but undefined or null loosely compared to anything else is false – other than the one exception of document.all, which we deal with in prose.
Update the accompanying example to include bigint, and to remove unnecessary and distracting null and undefined comparisons (obviously new String('0') == null and new String('0') == undefined are false; we don’t need to show an example of that).

This change refactors the entire “Loose equality using ==” section in the “Equality comparisons and sameness” article — with the goal of improving its usability, and at the same time fixing some technical problems with it. * Split the giant loose-equality table into a series of individual tables * Use &nsbp; in comparison formulas, to prevent bad/ugly breaks that otherwise occur in the tables. * Remove all the style attributes from the loose-equality tables (they are unnecessary, and we’d not be able to have styles in it when we move the table source to being markdown). * Make it explicit that the comparisons are to the number, bigint, and string *primitives* — not their corresponding objects. (Otherwise, especially because it has Number, BigInt, String, and Boolean in titlecase, it looked like it was about the objects, not the primitives). * Remove unnecessary redundancy/over-emphasis about comparisons to undefined and null: It’s simple: undefined == null is true, but undefined or null loosely compared to anything else is false – other than the one exception of document.all, which we deal with in prose. * Update the accompanying example to include bigint, and to remove unnecessary and distracting null and undefined comparisons (obviously new String('0') == null and new String('0') == undefined are false; we don’t need to show an example of that).

wbamberg · 2021-04-16T06:08:58Z

Thanks for this! I ran out of time today but will take a look tomorrow.

wbamberg

Thanks @sideshowbarker ! I must admit I kind of ran out of steam with this page over in #4118, so I'm really happy to see your PR, which is a vast improvement.

I had a few comments/questions.

wbamberg · 2021-04-16T16:45:59Z

files/en-us/web/javascript/equality_comparisons_and_sameness/index.html

+<table class="standard-table">
+  <thead>
+    <tr>
+      <td>number</td>


Should these be <th>?

Should these be <th>?

Indeed yes. Changed them and pushed

wbamberg · 2021-04-16T16:46:59Z

files/en-us/web/javascript/equality_comparisons_and_sameness/index.html

+  </thead>
+  <tbody>
+    <tr>
+      <td><code>ℝ(A)&nbsp;=&nbsp;ℝ(B)</code></td>


I'm not sure why this one (and some other instances further down) seem to be using assignment. AIUI these should all be === or am I confused?

<td><code>ℝ(A) = ℝ(B)</code></td>

I'm not sure why this one (and some other instances further down) seem to be using assignment. AIUI these should all be === or am I confused?

That’s actually verbatim from step 13 of the “Abstract Equality Comparison” algorithm in the ES spec at https://tc39.es/ecma262/#sec-abstract-equality-comparison:

If Type(x) is BigInt and Type(y) is Number, or if Type(x) is Number and Type(y) is BigInt, then:

a. If x or y are any of NaN, +∞𝔽, or -∞𝔽, return false.

b. If ℝ(x) = ℝ(y), return true; otherwise return false.

So I think it’s kind of inherently confusing outside of reading it in context the algorithm in the spec — where it’s more clear that it’s an equality comparison, not an assignment operation. But I think it might be wrong to change is to === in MDN, because the operation being performed there isn’t a JavaScript operation on JavaScript operands but instead an spec-internally-defined operation on spec constructs (“mathematical values” https://tc39.es/ecma262/#mathematical-value).

Anyway, I’ve now pushed a change to replace it with ℝ(x) equals ℝ(y). That looks a bit odd but it seems better than keeping ℝ(x) = ℝ(y) as-is and continuing to confuse everybody — and also better than ℝ(x) === ℝ(y), which I’m not sure would be correct (for the reason explained above).

FWIW: Perhaps the triple-bar for identity would have been another option: https://en.wikipedia.org/wiki/Equals_sign#Related_symbols

To me as Mathematician, ℝ reads as the „domain of real numbers” (which includes positive and negative infinity, which are excluded in the definition used by TC39 hier).

But I'm not sure, whether I understand the spec hier correctly.

files/en-us/web/javascript/equality_comparisons_and_sameness/index.html

github-actions · 2021-04-17T01:02:40Z

Preview URLs

https://pr4133.content.dev.mdn.mozit.cloud/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness

Flaws

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

No flaws! 🎉

External URLs

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

http://ecma-international.org/ecma-262/5.1/ (3 times)
https://dorey.github.io/JavaScript-Equality-Table/ (1 time)
https://en.wikipedia.org/wiki/Liskov_substitution_principle (1 time)
https://tc39.es/ecma262/ (2 times)

github-actions · 2021-04-17T01:32:14Z

Preview URLs

https://pr4133.content.dev.mdn.mozit.cloud/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness

Flaws

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

No flaws! 🎉

External URLs

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

http://ecma-international.org/ecma-262/5.1/ (3 times)
https://dorey.github.io/JavaScript-Equality-Table/ (1 time)
https://en.wikipedia.org/wiki/Liskov_substitution_principle (1 time)
https://tc39.es/ecma262/ (2 times)

github-actions · 2021-04-17T01:33:47Z

Preview URLs

https://pr4133.content.dev.mdn.mozit.cloud/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness

Flaws

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

No flaws! 🎉

External URLs

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

http://ecma-international.org/ecma-262/5.1/ (3 times)
https://dorey.github.io/JavaScript-Equality-Table/ (1 time)
https://en.wikipedia.org/wiki/Liskov_substitution_principle (1 time)
https://tc39.es/ecma262/ (2 times)

github-actions · 2021-04-17T02:02:37Z

Preview URLs

https://pr4133.content.dev.mdn.mozit.cloud/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness

Flaws

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

No flaws! 🎉

External URLs

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

http://ecma-international.org/ecma-262/5.1/ (3 times)
https://dorey.github.io/JavaScript-Equality-Table/ (1 time)
https://en.wikipedia.org/wiki/Liskov_substitution_principle (1 time)
https://tc39.es/ecma262/ (2 times)

github-actions · 2021-04-17T02:05:11Z

Preview URLs

https://pr4133.content.dev.mdn.mozit.cloud/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness

Flaws

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

No flaws! 🎉

External URLs

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

http://ecma-international.org/ecma-262/5.1/ (3 times)
https://dorey.github.io/JavaScript-Equality-Table/ (1 time)
https://en.wikipedia.org/wiki/Liskov_substitution_principle (1 time)
https://tc39.es/ecma262/ (2 times)

github-actions · 2021-04-17T02:07:03Z

Preview URLs

https://pr4133.content.dev.mdn.mozit.cloud/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness

Flaws

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

No flaws! 🎉

External URLs

URL: /en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
Title: Equality comparisons and sameness
on GitHub

http://ecma-international.org/ecma-262/5.1/ (3 times)
https://dorey.github.io/JavaScript-Equality-Table/ (1 time)
https://en.wikipedia.org/wiki/Liskov_substitution_principle (1 time)
https://tc39.es/ecma262/ (2 times)

sideshowbarker · 2021-04-17T02:07:25Z

Will, thanks much for the detailed review — I think it’s resulted in some significant improvements. I believe I’ve responded to all the review comments, so this is back to you now for re-review.

wbamberg

Thanks for the clarifications @sideshowbarker and for dismembering this monster table!

wbamberg · 2021-04-17T03:58:25Z

With this I think there are now no style attributes left in the JS docs.

sideshowbarker · 2021-04-17T04:00:38Z

With this I think there are now no style attributes left in the JS docs.

w00t — nice work 🎉

sideshowbarker requested a review from a team as a code owner April 15, 2021 14:16

sideshowbarker requested review from Rumyra and removed request for a team April 15, 2021 14:16

sideshowbarker mentioned this pull request Apr 15, 2021

[Markdown] Remove inline styles from JS reference #4118

Merged

wbamberg reviewed Apr 16, 2021

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Use proper <th> for table headings

0c4963e

Change “ℝ(A) = ℝ(B)” to “ℝ(x) equals ℝ(y)”

7583784

sideshowbarker force-pushed the sideshowbarker/equality_comparisons_and_sameness-loose-equality-fixes branch from 980e5b4 to 7583784 Compare April 17, 2021 01:32

sideshowbarker added 2 commits April 17, 2021 11:00

Replace some var with const

54e91d7

Move up warning not to use loose comparison

139308e

Change Examples to Example

4b50104

sideshowbarker requested a review from wbamberg April 17, 2021 02:07

wbamberg approved these changes Apr 17, 2021

View reviewed changes

wbamberg merged commit a441e6e into main Apr 17, 2021

wbamberg deleted the sideshowbarker/equality_comparisons_and_sameness-loose-equality-fixes branch April 17, 2021 03:56

wbamberg mentioned this pull request Apr 20, 2021

[Markdown] Decide what to do with tables #4325

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Refactor “Loose equality using ==” #4133

Refactor “Loose equality using ==” #4133

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Refactor “Loose equality using ==” #4133

Refactor “Loose equality using ==” #4133

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