assertStyles

Prefer assert.ok() over assert() for explicit intent and better readability.

✅ This rule is included in the node stylistic and stylisticStrict presets.

Using assert.ok() aligns with other assert methods, ensuring consistency and making code easier to maintain and understand. The explicit method call clarifies the assertion’s purpose, making it immediately clear that a boolean check is being performed.

import 
function assert(value: unknown, message?: string | Error): asserts value
An alias of
assert.ok
.
@since ― v0.5.9
@param ― value The input that is checked for being truthy.
assert from "node:assert";

function assert(value: unknown, message?: string | Error): asserts value
An alias of
assert.ok
.
@since ― v0.5.9
@param ― value The input that is checked for being truthy.
assert(
function divide(a: number, b: number): number
divide(10, 2) === 5);

import { 
function assert.strict(value: unknown, message?: string | Error): asserts value
namespace assert.strict
export assert.strict
strict as 
function assert(value: unknown, message?: string | Error): asserts value
assert } from "node:assert";

function assert(value: unknown, message?: string | Error): asserts value
assert(
const value: unknown
value);

import 
function assert(value: unknown, message?: string | Error): asserts value
An alias of
assert.ok
.
@since ― v0.5.9
@param ― value The input that is checked for being truthy.
assert from "node:assert";

function assert(value: unknown, message?: string | Error): asserts value
An alias of
assert.ok
.
@since ― v0.5.9
@param ― value The input that is checked for being truthy.
assert.
function assert.ok(value: unknown, message?: string | Error): asserts value
Tests if value is truthy. It is equivalent to assert.equal(!!value, true, message).
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 AssertionError.
If no arguments are passed in at all message will be set to the string:'No value argument passed to `assert.ok()`'.
Be aware that in the repl the error message will be different to the one
thrown in a file! See below for further details.
import assert from 'node:assert/strict';

assert.ok(true);
// OK
assert.ok(1);
// OK

assert.ok();
// AssertionError: No value argument passed to `assert.ok()`

assert.ok(false, 'it\'s false');
// AssertionError: it's false

// In the repl:
assert.ok(typeof 123 === 'string');
// AssertionError: false == true

// In a file (e.g. test.js):
assert.ok(typeof 123 === 'string');
// AssertionError: The expression evaluated to a falsy value:
//
//   assert.ok(typeof 123 === 'string')

assert.ok(false);
// AssertionError: The expression evaluated to a falsy value:
//
//   assert.ok(false)

assert.ok(0);
// AssertionError: The expression evaluated to a falsy value:
//
//   assert.ok(0)
import assert from 'node:assert/strict';

// Using `assert()` works the same:
assert(0);
// AssertionError: The expression evaluated to a falsy value:
//
//   assert(0)
@since ― v0.1.21
ok(
function divide(a: number, b: number): number
divide(10, 2) === 5);

import { 
function assert.strict(value: unknown, message?: string | Error): asserts value
namespace assert.strict
export assert.strict
strict as 
function assert(value: unknown, message?: string | Error): asserts value
assert } from "node:assert";

function assert(value: unknown, message?: string | Error): asserts value
assert.
strict.ok(value: unknown, message?: string | Error): asserts value
export strict.ok
Tests if value is truthy. It is equivalent to assert.equal(!!value, true, message).
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 AssertionError.
If no arguments are passed in at all message will be set to the string:'No value argument passed to `assert.ok()`'.
Be aware that in the repl the error message will be different to the one
thrown in a file! See below for further details.
import assert from 'node:assert/strict';

assert.ok(true);
// OK
assert.ok(1);
// OK

assert.ok();
// AssertionError: No value argument passed to `assert.ok()`

assert.ok(false, 'it\'s false');
// AssertionError: it's false

// In the repl:
assert.ok(typeof 123 === 'string');
// AssertionError: false == true

// In a file (e.g. test.js):
assert.ok(typeof 123 === 'string');
// AssertionError: The expression evaluated to a falsy value:
//
//   assert.ok(typeof 123 === 'string')

assert.ok(false);
// AssertionError: The expression evaluated to a falsy value:
//
//   assert.ok(false)

assert.ok(0);
// AssertionError: The expression evaluated to a falsy value:
//
//   assert.ok(0)
import assert from 'node:assert/strict';

// Using `assert()` works the same:
assert(0);
// AssertionError: The expression evaluated to a falsy value:
//
//   assert(0)
@since ― v0.1.21
ok(
const value: unknown
value);

import 
function assert(value: unknown, message?: string | Error): asserts value
An alias of
assert.ok
.
@since ― v0.5.9
@param ― value The input that is checked for being truthy.
assert from "node:assert";

function assert(value: unknown, message?: string | Error): asserts value
An alias of
assert.ok
.
@since ― v0.5.9
@param ― value The input that is checked for being truthy.
assert.
function assert.strictEqual<unknown>(actual: unknown, expected: unknown, message?: string | Error): asserts actual is unknown
Tests strict equality between the actual and expected parameters as
determined by Object.is().
import assert from 'node:assert/strict';

assert.strictEqual(1, 2);
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
//
// 1 !== 2

assert.strictEqual(1, 1);
// OK

assert.strictEqual('Hello foobar', 'Hello World!');
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
// + actual - expected
//
// + 'Hello foobar'
// - 'Hello World!'
//          ^

const apples = 1;
const oranges = 2;
assert.strictEqual(apples, oranges, `apples ${apples} !== oranges ${oranges}`);
// AssertionError [ERR_ASSERTION]: apples 1 !== oranges 2

assert.strictEqual(1, '1', new TypeError('Inputs are not identical'));
// TypeError: Inputs are not identical
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.
@since ― v0.1.21
strictEqual(
const actual: unknown
actual, 
const expected: unknown
expected);
function assert(value: unknown, message?: string | Error): asserts value
An alias of
assert.ok
.
@since ― v0.5.9
@param ― value The input that is checked for being truthy.
assert.
function assert.deepStrictEqual<unknown>(actual: unknown, expected: unknown, message?: string | Error): asserts actual is unknown
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.
@since ― v1.2.0
deepStrictEqual(
const actual: unknown
actual, 
const expected: unknown
expected);

Options

This rule is not configurable.

When Not To Use It

If you have a strong preference for the shorter assert() syntax and find it clear enough in your codebase, you might choose not to enable this rule.

Equivalents in Other Linters

ESLint: unicorn/consistent-assert
Oxlint: unicorn/consistent-assert

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assertStyles

Examples

Options

When Not To Use It

Further Reading

Equivalents in Other Linters