Skip to content

Commit

Permalink
doc: improve assert documentation
Browse files Browse the repository at this point in the history 
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 <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Vse Mozhet Byt <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
  • Loading branch information
@BridgeAR @MylesBorins
BridgeAR authored and MylesBorins committed Mar 13, 2018
1 parent fed51b3 commit 5a78c6c
Showing 1 changed file with 44 additions and 47 deletions.
91 changes: 44 additions & 47 deletions doc/api/assert.md
View file
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

0 comments on commit 5a78c6c

Please sign in to comment.