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doc: improve assert documentation
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1) Separate all loose and strict functions.
2) Stronger outline the used comparison rules in (not)deepStrictEqual
3) Fix SameValue comparison info

Backport-PR-URL: #19230
PR-URL: #17002
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
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@BridgeAR @MylesBorins
BridgeAR authored and MylesBorins committed Mar 13, 2018
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Showing 1 changed file with 44 additions and 47 deletions.
91 changes: 44 additions & 47 deletions doc/api/assert.md
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Original file line number Diff line number Diff line change
Expand Up @@ -101,7 +101,7 @@ assert.deepEqual(obj1, obj4);
If the values are not equal, an `AssertionError` is thrown with a `message`
property set equal to the value of the `message` parameter. If the `message`
parameter is undefined, a default error message is assigned. If the `message`
parameter is an instance of an `Error` then it will be thrown instead of the
parameter is an instance of an [`Error`][] then it will be thrown instead of the
`AssertionError`.

## assert.deepStrictEqual(actual, expected[, message])
Expand Down Expand Up @@ -136,50 +136,50 @@ changes:
* `expected` {any}
* `message` {any}

Identical to [`assert.deepEqual()`][] with the following exceptions:
Tests for deep equality between the `actual` and `expected` parameters.
"Deep" equality means that the enumerable "own" properties of child objects
are recursively evaluated also by the following rules.

1. Primitive values besides `NaN` are compared using the [Strict Equality
Comparison][] ( `===` ). Set and Map values, Map keys and `NaN` are compared
using the [SameValueZero][] comparison (which means they are free of the
[caveats][]).
2. [`[[Prototype]]`][prototype-spec] of objects are compared using
### Comparison details

* Primitive values are compared using the [SameValue Comparison][], used by
[`Object.is()`][].
* [Type tags][Object.prototype.toString()] of objects should be the same.
* [`[[Prototype]]`][prototype-spec] of objects are compared using
the [Strict Equality Comparison][] too.
3. [Type tags][Object.prototype.toString()] of objects should be the same.
4. [Object wrappers][] are compared both as objects and unwrapped values.
5. `0` and `-0` are not considered equal.
6. Enumerable own [`Symbol`][] properties are compared as well.
* Only [enumerable "own" properties][] are considered.
* [`Error`][] names and messages are always compared, even if these are not
enumerable properties.
* Enumerable own [`Symbol`][] properties are compared as well.
* [Object wrappers][] are compared both as objects and unwrapped values.
* Object properties are compared unordered.
* Map keys and Set items are compared unordered.
* Recursion stops when both sides differ or both sides encounter a circular
reference.

```js
const assert = require('assert');

assert.deepEqual({ a: 1 }, { a: '1' });
// OK, because 1 == '1'

assert.deepStrictEqual({ a: 1 }, { a: '1' });
// AssertionError: { a: 1 } deepStrictEqual { a: '1' }
// because 1 !== '1' using strict equality
// because 1 !== '1' using SameValue comparison

// The following objects don't have own properties
const date = new Date();
const object = {};
const fakeDate = {};

Object.setPrototypeOf(fakeDate, Date.prototype);

assert.deepEqual(object, fakeDate);
// OK, doesn't check [[Prototype]]
assert.deepStrictEqual(object, fakeDate);
// AssertionError: {} deepStrictEqual Date {}
// Different [[Prototype]]

assert.deepEqual(date, fakeDate);
// OK, doesn't check type tags
assert.deepStrictEqual(date, fakeDate);
// AssertionError: 2017-03-11T14:25:31.849Z deepStrictEqual Date {}
// Different type tags

assert.deepStrictEqual(NaN, NaN);
// OK, because of the SameValueZero comparison
// OK, because of the SameValue comparison

assert.deepStrictEqual(new Number(1), new Number(2));
// Fails because the wrapped number is unwrapped and compared as well.
Expand All @@ -202,7 +202,7 @@ assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });
If the values are not equal, an `AssertionError` is thrown with a `message`
property set equal to the value of the `message` parameter. If the `message`
parameter is undefined, a default error message is assigned. If the `message`
parameter is an instance of an `Error` then it will be thrown instead of the
parameter is an instance of an [`Error`][] then it will be thrown instead of the
`AssertionError`.

## assert.doesNotThrow(block[, error][, message])
Expand Down Expand Up @@ -298,7 +298,7 @@ assert.equal({ a: { b: 1 } }, { a: { b: 1 } });
If the values are not equal, an `AssertionError` is thrown with a `message`
property set equal to the value of the `message` parameter. If the `message`
parameter is undefined, a default error message is assigned. If the `message`
parameter is an instance of an `Error` then it will be thrown instead of the
parameter is an instance of an [`Error`][] then it will be thrown instead of the
`AssertionError`.

## assert.fail([message])
Expand All @@ -314,7 +314,7 @@ added: v0.1.21

Throws an `AssertionError`. If `message` is falsy, the error message is set as
the values of `actual` and `expected` separated by the provided `operator`. If
the `message` parameter is an instance of an `Error` then it will be thrown
the `message` parameter is an instance of an [`Error`][] then it will be thrown
instead of the `AssertionError`. If just the two `actual` and `expected`
arguments are provided, `operator` will default to `'!='`. If `message` is
provided only it will be used as the error message, the other arguments will be
Expand Down Expand Up @@ -451,7 +451,7 @@ assert.notDeepEqual(obj1, obj4);
If the values are deeply equal, an `AssertionError` is thrown with a `message`
property set equal to the value of the `message` parameter. If the `message`
parameter is undefined, a default error message is assigned. If the `message`
parameter is an instance of an `Error` then it will be thrown instead of the
parameter is an instance of an [`Error`][] then it will be thrown instead of the
`AssertionError`.

## assert.notDeepStrictEqual(actual, expected[, message])
Expand Down Expand Up @@ -491,18 +491,15 @@ Tests for deep strict inequality. Opposite of [`assert.deepStrictEqual()`][].
```js
const assert = require('assert');

assert.notDeepEqual({ a: 1 }, { a: '1' });
// AssertionError: { a: 1 } notDeepEqual { a: '1' }

assert.notDeepStrictEqual({ a: 1 }, { a: '1' });
// OK
```

If the values are deeply and strictly equal, an `AssertionError` is thrown with
a `message` property set equal to the value of the `message` parameter. If the
`message` parameter is undefined, a default error message is assigned. If the
`message` parameter is an instance of an `Error` then it will be thrown instead
of the `AssertionError`.
`message` parameter is an instance of an [`Error`][] then it will be thrown
instead of the `AssertionError`.

## assert.notEqual(actual, expected[, message])
<!-- YAML
Expand All @@ -528,10 +525,10 @@ assert.notEqual(1, '1');
// AssertionError: 1 != '1'
```

If the values are equal, an `AssertionError` is thrown with a `message`
property set equal to the value of the `message` parameter. If the `message`
parameter is undefined, a default error message is assigned. If the `message`
parameter is an instance of an `Error` then it will be thrown instead of the
If the values are equal, an `AssertionError` is thrown with a `message` property
set equal to the value of the `message` parameter. If the `message` parameter is
undefined, a default error message is assigned. If the `message` parameter is an
instance of an [`Error`][] then it will be thrown instead of the
`AssertionError`.

## assert.notStrictEqual(actual, expected[, message])
Expand All @@ -542,8 +539,8 @@ added: v0.1.21
* `expected` {any}
* `message` {any}

Tests strict inequality as determined by the [Strict Equality Comparison][]
( `!==` ).
Tests strict inequality between the `actual` and `expected` parameters as
determined by the [SameValue Comparison][].

```js
const assert = require('assert');
Expand All @@ -558,11 +555,11 @@ assert.notStrictEqual(1, '1');
// OK
```

If the values are strictly equal, an `AssertionError` is thrown with a
`message` property set equal to the value of the `message` parameter. If the
`message` parameter is undefined, a default error message is assigned. If the
`message` parameter is an instance of an `Error` then it will be thrown instead
of the `AssertionError`.
If the values are strictly equal, an `AssertionError` is thrown with a `message`
property set equal to the value of the `message` parameter. If the `message`
parameter is undefined, a default error message is assigned. If the `message`
parameter is an instance of an [`Error`][] then it will be thrown instead of the
`AssertionError`.

## assert.ok(value[, message])
<!-- YAML
Expand All @@ -577,7 +574,7 @@ Tests if `value` is truthy. It is equivalent to
If `value` is not truthy, an `AssertionError` is thrown with a `message`
property set equal to the value of the `message` parameter. If the `message`
parameter is `undefined`, a default error message is assigned. If the `message`
parameter is an instance of an `Error` then it will be thrown instead of the
parameter is an instance of an [`Error`][] then it will be thrown instead of the
`AssertionError`.

```js
Expand All @@ -603,8 +600,8 @@ added: v0.1.21
* `expected` {any}
* `message` {any}

Tests strict equality as determined by the [Strict Equality Comparison][]
( `===` ).
Tests strict equality between the `actual` and `expected` parameters as
determined by the [SameValue Comparison][].

```js
const assert = require('assert');
Expand All @@ -622,8 +619,8 @@ assert.strictEqual(1, '1');
If the values are not strictly equal, an `AssertionError` is thrown with a
`message` property set equal to the value of the `message` parameter. If the
`message` parameter is undefined, a default error message is assigned. If the
`message` parameter is an instance of an `Error` then it will be thrown instead
of the `AssertionError`.
`message` parameter is an instance of an [`Error`][] then it will be thrown
instead of the `AssertionError`.

## assert.throws(block[, error][, message])
<!-- YAML
Expand Down Expand Up @@ -736,8 +733,8 @@ For more information, see
[Abstract Equality Comparison]: https://tc39.github.io/ecma262/#sec-abstract-equality-comparison
[Object.prototype.toString()]: https://tc39.github.io/ecma262/#sec-object.prototype.tostring
[SameValueZero]: https://tc39.github.io/ecma262/#sec-samevaluezero
[SameValue Comparison]: https://tc39.github.io/ecma262/#sec-samevalue
[Strict Equality Comparison]: https://tc39.github.io/ecma262/#sec-strict-equality-comparison
[caveats]: #assert_caveats
[enumerable "own" properties]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties
[mdn-equality-guide]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
[prototype-spec]: https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots
Expand Down

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