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doc: `WeakSet` and `WeakMap` comparison details 

PR-URL: https://github.com/nodejs/node/pull/56648
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
pull/55341/merge
Shreyans Pathak 2025-01-20 15:18:21 -05:00 committed by GitHub
parent fdad2fa66e
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doc/api/assert.md
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@ -804,8 +804,10 @@ are recursively evaluated also by the following rules.
* [`Map`][] keys and [`Set`][] items are compared unordered.
* Recursion stops when both sides differ or both sides encounter a circular
reference.
* [`WeakMap`][] and [`WeakSet`][] comparison does not rely on their values. See
below for further details.
* [`WeakMap`][] and [`WeakSet`][] instances are **not** compared structurally.
They are only equal if they reference the same object. Any comparison between
different `WeakMap` or `WeakSet` instances will result in inequality,
even if they contain the same entries.
* [`RegExp`][] lastIndex, flags, and source are always compared, even if these
are not enumerable properties.
@ -882,23 +884,40 @@ assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });
// }
const weakMap1 = new WeakMap();
const weakMap2 = new WeakMap([[{}, {}]]);
const weakMap3 = new WeakMap();
weakMap3.unequal = true;
const weakMap2 = new WeakMap();
const obj = {};
weakMap1.set(obj, 'value');
weakMap2.set(obj, 'value');
// Comparing different instances fails, even with same contents
assert.deepStrictEqual(weakMap1, weakMap2);
// OK, because it is impossible to compare the entries
// AssertionError: Values have same structure but are not reference-equal:
//
// WeakMap {
// <items unknown>
// }
// Fails because weakMap3 has a property that weakMap1 does not contain:
assert.deepStrictEqual(weakMap1, weakMap3);
// Comparing the same instance to itself succeeds
assert.deepStrictEqual(weakMap1, weakMap1);
// OK
const weakSet1 = new WeakSet();
const weakSet2 = new WeakSet();
weakSet1.add(obj);
weakSet2.add(obj);
// Comparing different instances fails, even with same contents
assert.deepStrictEqual(weakSet1, weakSet2);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// WeakMap {
// + [items unknown]
// - [items unknown],
// - unequal: true
// }
// + WeakSet { <items unknown> }
// - WeakSet { <items unknown> }
// Comparing the same instance to itself succeeds
assert.deepStrictEqual(weakSet1, weakSet1);
// OK
```
```cjs
@ -974,23 +993,40 @@ assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });
// }
const weakMap1 = new WeakMap();
const weakMap2 = new WeakMap([[{}, {}]]);
const weakMap3 = new WeakMap();
weakMap3.unequal = true;
const weakMap2 = new WeakMap();
const obj = {};
weakMap1.set(obj, 'value');
weakMap2.set(obj, 'value');
// Comparing different instances fails, even with same contents
assert.deepStrictEqual(weakMap1, weakMap2);
// OK, because it is impossible to compare the entries
// AssertionError: Values have same structure but are not reference-equal:
//
// WeakMap {
// <items unknown>
// }
// Fails because weakMap3 has a property that weakMap1 does not contain:
assert.deepStrictEqual(weakMap1, weakMap3);
// Comparing the same instance to itself succeeds
assert.deepStrictEqual(weakMap1, weakMap1);
// OK
const weakSet1 = new WeakSet();
const weakSet2 = new WeakSet();
weakSet1.add(obj);
weakSet2.add(obj);
// Comparing different instances fails, even with same contents
assert.deepStrictEqual(weakSet1, weakSet2);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// WeakMap {
// + [items unknown]
// - [items unknown],
// - unequal: true
// }
// + WeakSet { <items unknown> }
// - WeakSet { <items unknown> }
// Comparing the same instance to itself succeeds
assert.deepStrictEqual(weakSet1, weakSet1);
// OK
```
If the values are not equal, an [`AssertionError`][] is thrown with a `message`