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doc: update Abstract Equality Comparison text in assert.md
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* Update link to ECMAScript specification
* Edit surprising-results material
* Other minor edits
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Trott committed Jan 2, 2022
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25 changes: 11 additions & 14 deletions doc/api/assert.md
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Expand Up @@ -104,7 +104,7 @@ more on color support in terminal environments, read the tty

## Legacy assertion mode

Legacy assertion mode uses the [Abstract Equality Comparison][] in:
Legacy assertion mode uses the [Abstract Equality Comparison][] (`==`) in:

* [`assert.deepEqual()`][]
* [`assert.equal()`][]
Expand All @@ -121,13 +121,11 @@ import assert from 'assert';
const assert = require('assert');
```

Whenever possible, use the [strict assertion mode][] instead. Otherwise, the
[Abstract Equality Comparison][] may cause surprising results. This is
especially true for [`assert.deepEqual()`][], where the comparison rules are
lax:
Legacy assertion mode may have surprising results, especially when using
[`assert.deepEqual()`][]:

```cjs
// WARNING: This does not throw an AssertionError!
// WARNING: This does not throw an AssertionError in legacy assertion mode!
assert.deepEqual(/a/gi, new Date());
```

Expand Down Expand Up @@ -526,8 +524,8 @@ are also recursively evaluated by the following rules.

### Comparison details

* Primitive values are compared with the [Abstract Equality Comparison][]
( `==` ) with the exception of `NaN`. It is treated as being identical in case
* Primitive values are compared with the `==` operator,
with the exception of `NaN`. It is treated as being identical in case
both sides are `NaN`.
* [Type tags][Object.prototype.toString()] of objects should be the same.
* Only [enumerable "own" properties][] are considered.
Expand All @@ -546,8 +544,7 @@ are also recursively evaluated by the following rules.
are not enumerable properties.

The following example does not throw an [`AssertionError`][] because the
primitives are considered equal by the [Abstract Equality Comparison][]
( `==` ).
primitives are compared using the `==` operator.

```mjs
import assert from 'assert';
Expand Down Expand Up @@ -1169,8 +1166,8 @@ An alias of [`assert.strictEqual()`][].
> Stability: 3 - Legacy: Use [`assert.strictEqual()`][] instead.
Tests shallow, coercive equality between the `actual` and `expected` parameters
using the [Abstract Equality Comparison][] ( `==` ). `NaN` is special handled
and treated as being identical in case both sides are `NaN`.
using the [Abstract Equality Comparison][] (`==`). `NaN` is specially handled
and treated as being identical if both sides are `NaN`.

```mjs
import assert from 'assert';
Expand Down Expand Up @@ -1688,7 +1685,7 @@ An alias of [`assert.notStrictEqual()`][].
> Stability: 3 - Legacy: Use [`assert.notStrictEqual()`][] instead.
Tests shallow, coercive inequality with the [Abstract Equality Comparison][]
(`!=` ). `NaN` is special handled and treated as being identical in case both
(`!=`). `NaN` is specially handled and treated as being identical in case both
sides are `NaN`.

```mjs
Expand Down Expand Up @@ -2448,7 +2445,7 @@ assert.throws(throwingFirst, /Second$/);
Due to the confusing error-prone notation, avoid a string as the second
argument.

[Abstract Equality Comparison]: https://tc39.github.io/ecma262/#sec-abstract-equality-comparison
[Abstract Equality Comparison]: https://262.ecma-international.org/#sec-abstract-equality-comparison
[Object wrappers]: https://developer.mozilla.org/en-US/docs/Glossary/Primitive#Primitive_wrapper_objects_in_JavaScript
[Object.prototype.toString()]: https://tc39.github.io/ecma262/#sec-object.prototype.tostring
[SameValue Comparison]: https://tc39.github.io/ecma262/#sec-samevalue
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