{ "type": "module", "source": "doc/api/assert.md", "modules": [ { "textRaw": "Assert", "name": "assert", "introduced_in": "v0.1.21", "stability": 2, "stabilityText": "Stable", "desc": "

The assert module provides a simple set of assertion tests that can be used to\ntest invariants.

\n

A strict and a legacy mode exist, while it is recommended to only use\nstrict mode.

\n

For more information about the used equality comparisons see\nMDN's guide on equality comparisons and sameness.

", "classes": [ { "textRaw": "Class: assert.AssertionError", "type": "class", "name": "assert.AssertionError", "desc": "

A subclass of Error that indicates the failure of an assertion. All errors\nthrown by the assert module will be instances of the AssertionError class.

", "signatures": [ { "params": [ { "textRaw": "`options` {Object}", "name": "options", "type": "Object", "options": [ { "textRaw": "`message` {string} If provided, the error message is going to be set to this value.", "name": "message", "type": "string", "desc": "If provided, the error message is going to be set to this value." }, { "textRaw": "`actual` {any} The `actual` property on the error instance is going to contain this value. Internally used for the `actual` error input in case e.g., [`assert.strictEqual()`] is used.", "name": "actual", "type": "any", "desc": "The `actual` property on the error instance is going to contain this value. Internally used for the `actual` error input in case e.g., [`assert.strictEqual()`] is used." }, { "textRaw": "`expected` {any} The `expected` property on the error instance is going to contain this value. Internally used for the `expected` error input in case e.g., [`assert.strictEqual()`] is used.", "name": "expected", "type": "any", "desc": "The `expected` property on the error instance is going to contain this value. Internally used for the `expected` error input in case e.g., [`assert.strictEqual()`] is used." }, { "textRaw": "`operator` {string} The `operator` property on the error instance is going to contain this value. Internally used to indicate what operation was used for comparison (or what assertion function triggered the error).", "name": "operator", "type": "string", "desc": "The `operator` property on the error instance is going to contain this value. Internally used to indicate what operation was used for comparison (or what assertion function triggered the error)." }, { "textRaw": "`stackStartFn` {Function} If provided, the generated stack trace is going to remove all frames up to the provided function.", "name": "stackStartFn", "type": "Function", "desc": "If provided, the generated stack trace is going to remove all frames up to the provided function." } ] } ], "desc": "

A subclass of Error that indicates the failure of an assertion.

\n

All instances contain the built-in Error properties (message and name)\nand:

\n\n
const assert = require('assert');\n\n// Generate an AssertionError to compare the error message later:\nconst { message } = new assert.AssertionError({\n  actual: 1,\n  expected: 2,\n  operator: 'strictEqual'\n});\n\n// Verify error output:\ntry {\n  assert.strictEqual(1, 2);\n} catch (err) {\n  assert(err instanceof assert.AssertionError);\n  assert.strictEqual(err.message, message);\n  assert.strictEqual(err.name, 'AssertionError [ERR_ASSERTION]');\n  assert.strictEqual(err.actual, 1);\n  assert.strictEqual(err.expected, 2);\n  assert.strictEqual(err.code, 'ERR_ASSERTION');\n  assert.strictEqual(err.operator, 'strictEqual');\n  assert.strictEqual(err.generatedMessage, true);\n}\n
" } ] } ], "modules": [ { "textRaw": "Strict mode", "name": "strict_mode", "meta": { "added": [ "v9.9.0" ], "changes": [ { "version": "v9.9.0", "pr-url": "https://github.com/nodejs/node/pull/17615", "description": "Added error diffs to the strict mode" }, { "version": "v9.9.0", "pr-url": "https://github.com/nodejs/node/pull/17002", "description": "Added strict mode to the assert module." } ] }, "desc": "

When using the strict mode, any assert function will use the equality used\nin the strict function mode. So assert.deepEqual() will, for example,\nwork the same as assert.deepStrictEqual().

\n

On top of that, error messages which involve objects produce an error diff\ninstead of displaying both objects. That is not the case for the legacy mode.

\n

It can be accessed using:

\n
const assert = require('assert').strict;\n
\n

Example error diff:

\n
const assert = require('assert').strict;\n\nassert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]);\n// AssertionError: Input A expected to strictly deep-equal input B:\n// + expected - actual ... Lines skipped\n//\n//   [\n//     [\n// ...\n//       2,\n// -     3\n// +     '3'\n//     ],\n// ...\n//     5\n//   ]\n
\n

To deactivate the colors, use the NODE_DISABLE_COLORS environment variable.\nPlease note that this will also deactivate the colors in the REPL.

", "type": "module", "displayName": "Strict mode" }, { "textRaw": "Legacy mode", "name": "legacy_mode", "stability": 0, "stabilityText": "Deprecated: Use strict mode instead.", "desc": "

When accessing assert directly instead of using the strict property, the\nAbstract Equality Comparison will be used for any function without \"strict\"\nin its name, such as assert.deepEqual().

\n

It can be accessed using:

\n
const assert = require('assert');\n
\n

It is recommended to use the strict mode instead as the\nAbstract Equality Comparison can often have surprising results. This is\nespecially true for assert.deepEqual(), where the comparison rules are\nlax:

\n
// WARNING: This does not throw an AssertionError!\nassert.deepEqual(/a/gi, new Date());\n
", "type": "module", "displayName": "Legacy mode" } ], "methods": [ { "textRaw": "assert(value[, message])", "type": "method", "name": "assert", "meta": { "added": [ "v0.5.9" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`value` {any} The input that is checked for being truthy.", "name": "value", "type": "any", "desc": "The input that is checked for being truthy." }, { "textRaw": "`message` {string|Error}", "name": "message", "type": "string|Error", "optional": true } ] } ], "desc": "

An alias of assert.ok().

" }, { "textRaw": "assert.deepEqual(actual, expected[, message])", "type": "method", "name": "deepEqual", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v9.0.0", "pr-url": "https://github.com/nodejs/node/pull/15001", "description": "The `Error` names and messages are now properly compared" }, { "version": "v8.0.0", "pr-url": "https://github.com/nodejs/node/pull/12142", "description": "The `Set` and `Map` content is also compared" }, { "version": "v6.4.0, v4.7.1", "pr-url": "https://github.com/nodejs/node/pull/8002", "description": "Typed array slices are handled correctly now." }, { "version": "v6.1.0, v4.5.0", "pr-url": "https://github.com/nodejs/node/pull/6432", "description": "Objects with circular references can be used as inputs now." }, { "version": "v5.10.1, v4.4.3", "pr-url": "https://github.com/nodejs/node/pull/5910", "description": "Handle non-`Uint8Array` typed arrays correctly." } ] }, "signatures": [ { "params": [ { "textRaw": "`actual` {any}", "name": "actual", "type": "any" }, { "textRaw": "`expected` {any}", "name": "expected", "type": "any" }, { "textRaw": "`message` {string|Error}", "name": "message", "type": "string|Error", "optional": true } ] } ], "desc": "

Strict mode

\n

An alias of assert.deepStrictEqual().

\n

Legacy mode

\n
\n

Stability: 0 - Deprecated: Use assert.deepStrictEqual() instead.

\n
\n

Tests for deep equality between the actual and expected parameters.\nPrimitive values are compared with the Abstract Equality Comparison\n( == ).

\n

Only enumerable \"own\" properties are considered. The\nassert.deepEqual() implementation does not test the\n[[Prototype]] of objects or enumerable own Symbol\nproperties. For such checks, consider using assert.deepStrictEqual()\ninstead. assert.deepEqual() can have potentially surprising results. The\nfollowing example does not throw an AssertionError because the properties on\nthe RegExp object are not enumerable:

\n
// WARNING: This does not throw an AssertionError!\nassert.deepEqual(/a/gi, new Date());\n
\n

An exception is made for Map and Set. Maps and Sets have their\ncontained items compared too, as expected.

\n

\"Deep\" equality means that the enumerable \"own\" properties of child objects\nare evaluated also:

\n
const assert = require('assert');\n\nconst obj1 = {\n  a: {\n    b: 1\n  }\n};\nconst obj2 = {\n  a: {\n    b: 2\n  }\n};\nconst obj3 = {\n  a: {\n    b: 1\n  }\n};\nconst obj4 = Object.create(obj1);\n\nassert.deepEqual(obj1, obj1);\n// OK\n\n// Values of b are different:\nassert.deepEqual(obj1, obj2);\n// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }\n\nassert.deepEqual(obj1, obj3);\n// OK\n\n// Prototypes are ignored:\nassert.deepEqual(obj1, obj4);\n// AssertionError: { a: { b: 1 } } deepEqual {}\n
\n

If the values are not equal, an AssertionError is thrown with a message\nproperty set equal to the value of the message parameter. If the message\nparameter is undefined, a default error message is assigned. If the message\nparameter is an instance of an Error then it will be thrown instead of the\nAssertionError.

" }, { "textRaw": "assert.deepStrictEqual(actual, expected[, message])", "type": "method", "name": "deepStrictEqual", "meta": { "added": [ "v1.2.0" ], "changes": [ { "version": "v9.0.0", "pr-url": "https://github.com/nodejs/node/pull/15169", "description": "Enumerable symbol properties are now compared." }, { "version": "v9.0.0", "pr-url": "https://github.com/nodejs/node/pull/15036", "description": "The `NaN` is now compared using the [SameValueZero](https://tc39.github.io/ecma262/#sec-samevaluezero) comparison." }, { "version": "v8.5.0", "pr-url": "https://github.com/nodejs/node/pull/15001", "description": "The `Error` names and messages are now properly compared" }, { "version": "v8.0.0", "pr-url": "https://github.com/nodejs/node/pull/12142", "description": "The `Set` and `Map` content is also compared" }, { "version": "v6.4.0, v4.7.1", "pr-url": "https://github.com/nodejs/node/pull/8002", "description": "Typed array slices are handled correctly now." }, { "version": "v6.1.0", "pr-url": "https://github.com/nodejs/node/pull/6432", "description": "Objects with circular references can be used as inputs now." }, { "version": "v5.10.1, v4.4.3", "pr-url": "https://github.com/nodejs/node/pull/5910", "description": "Handle non-`Uint8Array` typed arrays correctly." } ] }, "signatures": [ { "params": [ { "textRaw": "`actual` {any}", "name": "actual", "type": "any" }, { "textRaw": "`expected` {any}", "name": "expected", "type": "any" }, { "textRaw": "`message` {string|Error}", "name": "message", "type": "string|Error", "optional": true } ] } ], "desc": "

Tests for deep equality between the actual and expected parameters.\n\"Deep\" equality means that the enumerable \"own\" properties of child objects\nare recursively evaluated also by the following rules.

", "modules": [ { "textRaw": "Comparison details", "name": "comparison_details", "desc": "\n
const assert = require('assert').strict;\n\n// This fails because 1 !== '1'.\nassert.deepStrictEqual({ a: 1 }, { a: '1' });\n// AssertionError: Input A expected to strictly deep-equal input B:\n// + expected - actual\n//   {\n// -   a: 1\n// +   a: '1'\n//   }\n\n// The following objects don't have own properties\nconst date = new Date();\nconst object = {};\nconst fakeDate = {};\nObject.setPrototypeOf(fakeDate, Date.prototype);\n\n// Different [[Prototype]]:\nassert.deepStrictEqual(object, fakeDate);\n// AssertionError: Input A expected to strictly deep-equal input B:\n// + expected - actual\n// - {}\n// + Date {}\n\n// Different type tags:\nassert.deepStrictEqual(date, fakeDate);\n// AssertionError: Input A expected to strictly deep-equal input B:\n// + expected - actual\n// - 2018-04-26T00:49:08.604Z\n// + Date {}\n\nassert.deepStrictEqual(NaN, NaN);\n// OK, because of the SameValue comparison\n\n// Different unwrapped numbers:\nassert.deepStrictEqual(new Number(1), new Number(2));\n// AssertionError: Input A expected to strictly deep-equal input B:\n// + expected - actual\n// - [Number: 1]\n// + [Number: 2]\n\nassert.deepStrictEqual(new String('foo'), Object('foo'));\n// OK because the object and the string are identical when unwrapped.\n\nassert.deepStrictEqual(-0, -0);\n// OK\n\n// Different zeros using the SameValue Comparison:\nassert.deepStrictEqual(0, -0);\n// AssertionError: Input A expected to strictly deep-equal input B:\n// + expected - actual\n// - 0\n// + -0\n\nconst symbol1 = Symbol();\nconst symbol2 = Symbol();\nassert.deepStrictEqual({ [symbol1]: 1 }, { [symbol1]: 1 });\n// OK, because it is the same symbol on both objects.\nassert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });\n// AssertionError [ERR_ASSERTION]: Input objects not identical:\n// {\n//   [Symbol()]: 1\n// }\n\nconst weakMap1 = new WeakMap();\nconst weakMap2 = new WeakMap([[{}, {}]]);\nconst weakMap3 = new WeakMap();\nweakMap3.unequal = true;\n\nassert.deepStrictEqual(weakMap1, weakMap2);\n// OK, because it is impossible to compare the entries\n\n// Fails because weakMap3 has a property that weakMap1 does not contain:\nassert.deepStrictEqual(weakMap1, weakMap3);\n// AssertionError: Input A expected to strictly deep-equal input B:\n// + expected - actual\n//   WeakMap {\n// -   [items unknown]\n// +   [items unknown],\n// +   unequal: true\n//   }\n
\n

If the values are not equal, an AssertionError is thrown with a message\nproperty set equal to the value of the message parameter. If the message\nparameter is undefined, a default error message is assigned. If the message\nparameter is an instance of an Error then it will be thrown instead of the\nAssertionError.

", "type": "module", "displayName": "Comparison details" } ] }, { "textRaw": "assert.doesNotReject(asyncFn[, error][, message])", "type": "method", "name": "doesNotReject", "meta": { "added": [ "v10.0.0" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`asyncFn` {Function|Promise}", "name": "asyncFn", "type": "Function|Promise" }, { "textRaw": "`error` {RegExp|Function}", "name": "error", "type": "RegExp|Function", "optional": true }, { "textRaw": "`message` {string}", "name": "message", "type": "string", "optional": true } ] } ], "desc": "

Awaits the asyncFn promise or, if asyncFn is a function, immediately\ncalls the function and awaits the returned promise to complete. It will then\ncheck that the promise is not rejected.

\n

If asyncFn is a function and it throws an error synchronously,\nassert.doesNotReject() will return a rejected Promise with that error. If\nthe function does not return a promise, assert.doesNotReject() will return a\nrejected Promise with an ERR_INVALID_RETURN_VALUE error. In both cases\nthe error handler is skipped.

\n

Using assert.doesNotReject() is actually not useful because there is little\nbenefit in catching a rejection and then rejecting it again. Instead, consider\nadding a comment next to the specific code path that should not reject and keep\nerror messages as expressive as possible.

\n

If specified, error can be a Class, RegExp or a validation\nfunction. See assert.throws() for more details.

\n

Besides the async nature to await the completion behaves identically to\nassert.doesNotThrow().

\n
(async () => {\n  await assert.doesNotReject(\n    async () => {\n      throw new TypeError('Wrong value');\n    },\n    SyntaxError\n  );\n})();\n
\n
assert.doesNotReject(Promise.reject(new TypeError('Wrong value')))\n  .then(() => {\n    // ...\n  });\n
" }, { "textRaw": "assert.doesNotThrow(fn[, error][, message])", "type": "method", "name": "doesNotThrow", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v5.11.0, v4.4.5", "pr-url": "https://github.com/nodejs/node/pull/2407", "description": "The `message` parameter is respected now." }, { "version": "v4.2.0", "pr-url": "https://github.com/nodejs/node/pull/3276", "description": "The `error` parameter can now be an arrow function." } ] }, "signatures": [ { "params": [ { "textRaw": "`fn` {Function}", "name": "fn", "type": "Function" }, { "textRaw": "`error` {RegExp|Function}", "name": "error", "type": "RegExp|Function", "optional": true }, { "textRaw": "`message` {string}", "name": "message", "type": "string", "optional": true } ] } ], "desc": "

Asserts that the function fn does not throw an error.

\n

Using assert.doesNotThrow() is actually not useful because there\nis no benefit in catching an error and then rethrowing it. Instead, consider\nadding a comment next to the specific code path that should not throw and keep\nerror messages as expressive as possible.

\n

When assert.doesNotThrow() is called, it will immediately call the fn\nfunction.

\n

If an error is thrown and it is the same type as that specified by the error\nparameter, then an AssertionError is thrown. If the error is of a different\ntype, or if the error parameter is undefined, the error is propagated back\nto the caller.

\n

If specified, error can be a Class, RegExp or a validation\nfunction. See assert.throws() for more details.

\n

The following, for instance, will throw the TypeError because there is no\nmatching error type in the assertion:

\n\n
assert.doesNotThrow(\n  () => {\n    throw new TypeError('Wrong value');\n  },\n  SyntaxError\n);\n
\n

However, the following will result in an AssertionError with the message\n'Got unwanted exception...':

\n\n
assert.doesNotThrow(\n  () => {\n    throw new TypeError('Wrong value');\n  },\n  TypeError\n);\n
\n

If an AssertionError is thrown and a value is provided for the message\nparameter, the value of message will be appended to the AssertionError\nmessage:

\n\n
assert.doesNotThrow(\n  () => {\n    throw new TypeError('Wrong value');\n  },\n  /Wrong value/,\n  'Whoops'\n);\n// Throws: AssertionError: Got unwanted exception: Whoops\n
" }, { "textRaw": "assert.equal(actual, expected[, message])", "type": "method", "name": "equal", "meta": { "added": [ "v0.1.21" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`actual` {any}", "name": "actual", "type": "any" }, { "textRaw": "`expected` {any}", "name": "expected", "type": "any" }, { "textRaw": "`message` {string|Error}", "name": "message", "type": "string|Error", "optional": true } ] } ], "desc": "

Strict mode

\n

An alias of assert.strictEqual().

\n

Legacy mode

\n
\n

Stability: 0 - Deprecated: Use assert.strictEqual() instead.

\n
\n

Tests shallow, coercive equality between the actual and expected parameters\nusing the Abstract Equality Comparison ( == ).

\n
const assert = require('assert');\n\nassert.equal(1, 1);\n// OK, 1 == 1\nassert.equal(1, '1');\n// OK, 1 == '1'\n\nassert.equal(1, 2);\n// AssertionError: 1 == 2\nassert.equal({ a: { b: 1 } }, { a: { b: 1 } });\n// AssertionError: { a: { b: 1 } } == { a: { b: 1 } }\n
\n

If the values are not equal, an AssertionError is thrown with a message\nproperty set equal to the value of the message parameter. If the message\nparameter is undefined, a default error message is assigned. If the message\nparameter is an instance of an Error then it will be thrown instead of the\nAssertionError.

" }, { "textRaw": "assert.fail([message])", "type": "method", "name": "fail", "meta": { "added": [ "v0.1.21" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`message` {string|Error} **Default:** `'Failed'`", "name": "message", "type": "string|Error", "default": "`'Failed'`", "optional": true } ] } ], "desc": "

Throws an AssertionError with the provided error message or a default error\nmessage. If the message parameter is an instance of an Error then it\nwill be thrown instead of the AssertionError.

\n
const assert = require('assert').strict;\n\nassert.fail();\n// AssertionError [ERR_ASSERTION]: Failed\n\nassert.fail('boom');\n// AssertionError [ERR_ASSERTION]: boom\n\nassert.fail(new TypeError('need array'));\n// TypeError: need array\n
\n

Using assert.fail() with more than two arguments is possible but deprecated.\nSee below for further details.

" }, { "textRaw": "assert.fail(actual, expected[, message[, operator[, stackStartFn]]])", "type": "method", "name": "fail", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v10.0.0", "pr-url": "https://github.com/nodejs/node/pull/18418", "description": "Calling `assert.fail()` with more than one argument is deprecated and emits a warning." } ] }, "stability": 0, "stabilityText": "Deprecated: Use `assert.fail([message])` or other assert\nfunctions instead.", "signatures": [ { "params": [ { "textRaw": "`actual` {any}", "name": "actual", "type": "any" }, { "textRaw": "`expected` {any}", "name": "expected", "type": "any" }, { "textRaw": "`message` {string|Error}", "name": "message", "type": "string|Error", "optional": true }, { "textRaw": "`operator` {string} **Default:** `'!='`", "name": "operator", "type": "string", "default": "`'!='`", "optional": true }, { "textRaw": "`stackStartFn` {Function} **Default:** `assert.fail`", "name": "stackStartFn", "type": "Function", "default": "`assert.fail`", "optional": true } ] } ], "desc": "

If message is falsy, the error message is set as the values of actual and\nexpected separated by the provided operator. If just the two actual and\nexpected arguments are provided, operator will default to '!='. If\nmessage is provided as third argument it will be used as the error message and\nthe other arguments will be stored as properties on the thrown object. If\nstackStartFn is provided, all stack frames above that function will be\nremoved from stacktrace (see Error.captureStackTrace). If no arguments are\ngiven, the default message Failed will be used.

\n
const assert = require('assert').strict;\n\nassert.fail('a', 'b');\n// AssertionError [ERR_ASSERTION]: 'a' != 'b'\n\nassert.fail(1, 2, undefined, '>');\n// AssertionError [ERR_ASSERTION]: 1 > 2\n\nassert.fail(1, 2, 'fail');\n// AssertionError [ERR_ASSERTION]: fail\n\nassert.fail(1, 2, 'whoops', '>');\n// AssertionError [ERR_ASSERTION]: whoops\n\nassert.fail(1, 2, new TypeError('need array'));\n// TypeError: need array\n
\n

In the last three cases actual, expected, and operator have no\ninfluence on the error message.

\n

Example use of stackStartFn for truncating the exception's stacktrace:

\n
function suppressFrame() {\n  assert.fail('a', 'b', undefined, '!==', suppressFrame);\n}\nsuppressFrame();\n// AssertionError [ERR_ASSERTION]: 'a' !== 'b'\n//     at repl:1:1\n//     at ContextifyScript.Script.runInThisContext (vm.js:44:33)\n//     ...\n
" }, { "textRaw": "assert.ifError(value)", "type": "method", "name": "ifError", "meta": { "added": [ "v0.1.97" ], "changes": [ { "version": "v10.0.0", "pr-url": "https://github.com/nodejs/node/pull/18247", "description": "Instead of throwing the original error it is now wrapped into an `AssertionError` that contains the full stack trace." }, { "version": "v10.0.0", "pr-url": "https://github.com/nodejs/node/pull/18247", "description": "Value may now only be `undefined` or `null`. Before all falsy values were handled the same as `null` and did not throw." } ] }, "signatures": [ { "params": [ { "textRaw": "`value` {any}", "name": "value", "type": "any" } ] } ], "desc": "

Throws value if value is not undefined or null. This is useful when\ntesting the error argument in callbacks. The stack trace contains all frames\nfrom the error passed to ifError() including the potential new frames for\nifError() itself.

\n
const assert = require('assert').strict;\n\nassert.ifError(null);\n// OK\nassert.ifError(0);\n// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0\nassert.ifError('error');\n// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error'\nassert.ifError(new Error());\n// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error\n\n// Create some random error frames.\nlet err;\n(function errorFrame() {\n  err = new Error('test error');\n})();\n\n(function ifErrorFrame() {\n  assert.ifError(err);\n})();\n// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error\n//     at ifErrorFrame\n//     at errorFrame\n
" }, { "textRaw": "assert.notDeepEqual(actual, expected[, message])", "type": "method", "name": "notDeepEqual", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v9.0.0", "pr-url": "https://github.com/nodejs/node/pull/15001", "description": "The `Error` names and messages are now properly compared" }, { "version": "v8.0.0", "pr-url": "https://github.com/nodejs/node/pull/12142", "description": "The `Set` and `Map` content is also compared" }, { "version": "v6.4.0, v4.7.1", "pr-url": "https://github.com/nodejs/node/pull/8002", "description": "Typed array slices are handled correctly now." }, { "version": "v6.1.0, v4.5.0", "pr-url": "https://github.com/nodejs/node/pull/6432", "description": "Objects with circular references can be used as inputs now." }, { "version": "v5.10.1, v4.4.3", "pr-url": "https://github.com/nodejs/node/pull/5910", "description": "Handle non-`Uint8Array` typed arrays correctly." } ] }, "signatures": [ { "params": [ { "textRaw": "`actual` {any}", "name": "actual", "type": "any" }, { "textRaw": "`expected` {any}", "name": "expected", "type": "any" }, { "textRaw": "`message` {string|Error}", "name": "message", "type": "string|Error", "optional": true } ] } ], "desc": "

Strict mode

\n

An alias of assert.notDeepStrictEqual().

\n

Legacy mode

\n
\n

Stability: 0 - Deprecated: Use assert.notDeepStrictEqual() instead.

\n
\n

Tests for any deep inequality. Opposite of assert.deepEqual().

\n
const assert = require('assert');\n\nconst obj1 = {\n  a: {\n    b: 1\n  }\n};\nconst obj2 = {\n  a: {\n    b: 2\n  }\n};\nconst obj3 = {\n  a: {\n    b: 1\n  }\n};\nconst obj4 = Object.create(obj1);\n\nassert.notDeepEqual(obj1, obj1);\n// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }\n\nassert.notDeepEqual(obj1, obj2);\n// OK\n\nassert.notDeepEqual(obj1, obj3);\n// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }\n\nassert.notDeepEqual(obj1, obj4);\n// OK\n
\n

If the values are deeply equal, an AssertionError is thrown with a message\nproperty set equal to the value of the message parameter. If the message\nparameter is undefined, a default error message is assigned. If the message\nparameter is an instance of an Error then it will be thrown instead of the\nAssertionError.

" }, { "textRaw": "assert.notDeepStrictEqual(actual, expected[, message])", "type": "method", "name": "notDeepStrictEqual", "meta": { "added": [ "v1.2.0" ], "changes": [ { "version": "v9.0.0", "pr-url": "https://github.com/nodejs/node/pull/15398", "description": "The `-0` and `+0` are not considered equal anymore." }, { "version": "v9.0.0", "pr-url": "https://github.com/nodejs/node/pull/15036", "description": "The `NaN` is now compared using the [SameValueZero](https://tc39.github.io/ecma262/#sec-samevaluezero) comparison." }, { "version": "v9.0.0", "pr-url": "https://github.com/nodejs/node/pull/15001", "description": "The `Error` names and messages are now properly compared" }, { "version": "v8.0.0", "pr-url": "https://github.com/nodejs/node/pull/12142", "description": "The `Set` and `Map` content is also compared" }, { "version": "v6.4.0, v4.7.1", "pr-url": "https://github.com/nodejs/node/pull/8002", "description": "Typed array slices are handled correctly now." }, { "version": "v6.1.0", "pr-url": "https://github.com/nodejs/node/pull/6432", "description": "Objects with circular references can be used as inputs now." }, { "version": "v5.10.1, v4.4.3", "pr-url": "https://github.com/nodejs/node/pull/5910", "description": "Handle non-`Uint8Array` typed arrays correctly." } ] }, "signatures": [ { "params": [ { "textRaw": "`actual` {any}", "name": "actual", "type": "any" }, { "textRaw": "`expected` {any}", "name": "expected", "type": "any" }, { "textRaw": "`message` {string|Error}", "name": "message", "type": "string|Error", "optional": true } ] } ], "desc": "

Tests for deep strict inequality. Opposite of assert.deepStrictEqual().

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const assert = require('assert').strict;\n\nassert.notDeepStrictEqual({ a: 1 }, { a: '1' });\n// OK\n
\n

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

" }, { "textRaw": "assert.notEqual(actual, expected[, message])", "type": "method", "name": "notEqual", "meta": { "added": [ "v0.1.21" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`actual` {any}", "name": "actual", "type": "any" }, { "textRaw": "`expected` {any}", "name": "expected", "type": "any" }, { "textRaw": "`message` {string|Error}", "name": "message", "type": "string|Error", "optional": true } ] } ], "desc": "

Strict mode

\n

An alias of assert.notStrictEqual().

\n

Legacy mode

\n
\n

Stability: 0 - Deprecated: Use assert.notStrictEqual() instead.

\n
\n

Tests shallow, coercive inequality with the Abstract Equality Comparison\n( != ).

\n
const assert = require('assert');\n\nassert.notEqual(1, 2);\n// OK\n\nassert.notEqual(1, 1);\n// AssertionError: 1 != 1\n\nassert.notEqual(1, '1');\n// AssertionError: 1 != '1'\n
\n

If the values are equal, an AssertionError is thrown with a message property\nset equal to the value of the message parameter. If the message parameter is\nundefined, a default error message is assigned. If the message parameter is an\ninstance of an Error then it will be thrown instead of the\nAssertionError.

" }, { "textRaw": "assert.notStrictEqual(actual, expected[, message])", "type": "method", "name": "notStrictEqual", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v10.0.0", "pr-url": "https://github.com/nodejs/node/pull/17003", "description": "Used comparison changed from Strict Equality to `Object.is()`" } ] }, "signatures": [ { "params": [ { "textRaw": "`actual` {any}", "name": "actual", "type": "any" }, { "textRaw": "`expected` {any}", "name": "expected", "type": "any" }, { "textRaw": "`message` {string|Error}", "name": "message", "type": "string|Error", "optional": true } ] } ], "desc": "

Tests strict inequality between the actual and expected parameters as\ndetermined by the SameValue Comparison.

\n
const assert = require('assert').strict;\n\nassert.notStrictEqual(1, 2);\n// OK\n\nassert.notStrictEqual(1, 1);\n// AssertionError [ERR_ASSERTION]: Identical input passed to notStrictEqual: 1\n\nassert.notStrictEqual(1, '1');\n// OK\n
\n

If the values are strictly equal, an AssertionError is thrown with a message\nproperty set equal to the value of the message parameter. If the message\nparameter is undefined, a default error message is assigned. If the message\nparameter is an instance of an Error then it will be thrown instead of the\nAssertionError.

" }, { "textRaw": "assert.ok(value[, message])", "type": "method", "name": "ok", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v10.0.0", "pr-url": "https://github.com/nodejs/node/pull/18319", "description": "The `assert.ok()` (no arguments) will now use a predefined error message." } ] }, "signatures": [ { "params": [ { "textRaw": "`value` {any}", "name": "value", "type": "any" }, { "textRaw": "`message` {string|Error}", "name": "message", "type": "string|Error", "optional": true } ] } ], "desc": "

Tests if value is truthy. It is equivalent to\nassert.equal(!!value, true, message).

\n

If value is not truthy, an AssertionError is thrown with a message\nproperty set equal to the value of the message parameter. If the message\nparameter is undefined, a default error message is assigned. If the message\nparameter is an instance of an Error then it will be thrown instead of the\nAssertionError.\nIf no arguments are passed in at all message will be set to the string:\n'No value argument passed to `assert.ok()`'.

\n

Be aware that in the repl the error message will be different to the one\nthrown in a file! See below for further details.

\n
const assert = require('assert').strict;\n\nassert.ok(true);\n// OK\nassert.ok(1);\n// OK\n\nassert.ok();\n// AssertionError: No value argument passed to `assert.ok()`\n\nassert.ok(false, 'it\\'s false');\n// AssertionError: it's false\n\n// In the repl:\nassert.ok(typeof 123 === 'string');\n// AssertionError: false == true\n\n// In a file (e.g. test.js):\nassert.ok(typeof 123 === 'string');\n// AssertionError: The expression evaluated to a falsy value:\n//\n//   assert.ok(typeof 123 === 'string')\n\nassert.ok(false);\n// AssertionError: The expression evaluated to a falsy value:\n//\n//   assert.ok(false)\n\nassert.ok(0);\n// AssertionError: The expression evaluated to a falsy value:\n//\n//   assert.ok(0)\n\n// Using `assert()` works the same:\nassert(0);\n// AssertionError: The expression evaluated to a falsy value:\n//\n//   assert(0)\n
" }, { "textRaw": "assert.rejects(asyncFn[, error][, message])", "type": "method", "name": "rejects", "meta": { "added": [ "v10.0.0" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`asyncFn` {Function|Promise}", "name": "asyncFn", "type": "Function|Promise" }, { "textRaw": "`error` {RegExp|Function|Object|Error}", "name": "error", "type": "RegExp|Function|Object|Error", "optional": true }, { "textRaw": "`message` {string}", "name": "message", "type": "string", "optional": true } ] } ], "desc": "

Awaits the asyncFn promise or, if asyncFn is a function, immediately\ncalls the function and awaits the returned promise to complete. It will then\ncheck that the promise is rejected.

\n

If asyncFn is a function and it throws an error synchronously,\nassert.rejects() will return a rejected Promise with that error. If the\nfunction does not return a promise, assert.rejects() will return a rejected\nPromise with an ERR_INVALID_RETURN_VALUE error. In both cases the error\nhandler is skipped.

\n

Besides the async nature to await the completion behaves identically to\nassert.throws().

\n

If specified, error can be a Class, RegExp, a validation function,\nan object where each property will be tested for, or an instance of error where\neach property will be tested for including the non-enumerable message and\nname properties.

\n

If specified, message will be the message provided by the AssertionError if\nthe asyncFn fails to reject.

\n
(async () => {\n  await assert.rejects(\n    async () => {\n      throw new TypeError('Wrong value');\n    },\n    {\n      name: 'TypeError',\n      message: 'Wrong value'\n    }\n  );\n})();\n
\n
assert.rejects(\n  Promise.reject(new Error('Wrong value')),\n  Error\n).then(() => {\n  // ...\n});\n
\n

Note that error cannot be a string. If a string is provided as the second\nargument, then error is assumed to be omitted and the string will be used for\nmessage instead. This can lead to easy-to-miss mistakes. Please read the\nexample in assert.throws() carefully if using a string as the second\nargument gets considered.

" }, { "textRaw": "assert.strictEqual(actual, expected[, message])", "type": "method", "name": "strictEqual", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v10.0.0", "pr-url": "https://github.com/nodejs/node/pull/17003", "description": "Used comparison changed from Strict Equality to `Object.is()`" } ] }, "signatures": [ { "params": [ { "textRaw": "`actual` {any}", "name": "actual", "type": "any" }, { "textRaw": "`expected` {any}", "name": "expected", "type": "any" }, { "textRaw": "`message` {string|Error}", "name": "message", "type": "string|Error", "optional": true } ] } ], "desc": "

Tests strict equality between the actual and expected parameters as\ndetermined by the SameValue Comparison.

\n
const assert = require('assert').strict;\n\nassert.strictEqual(1, 2);\n// AssertionError [ERR_ASSERTION]: Input A expected to strictly equal input B:\n// + expected - actual\n// - 1\n// + 2\n\nassert.strictEqual(1, 1);\n// OK\n\nassert.strictEqual(1, '1');\n// AssertionError [ERR_ASSERTION]: Input A expected to strictly equal input B:\n// + expected - actual\n// - 1\n// + '1'\n
\n

If the values are not strictly equal, an AssertionError is thrown with a\nmessage property set equal to the value of the message parameter. If the\nmessage parameter is undefined, a default error message is assigned. If the\nmessage parameter is an instance of an Error then it will be thrown\ninstead of the AssertionError.

" }, { "textRaw": "assert.throws(fn[, error][, message])", "type": "method", "name": "throws", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v10.2.0", "pr-url": "https://github.com/nodejs/node/pull/20485", "description": "The `error` parameter can be an object containing regular expressions now." }, { "version": "v9.9.0", "pr-url": "https://github.com/nodejs/node/pull/17584", "description": "The `error` parameter can now be an object as well." }, { "version": "v4.2.0", "pr-url": "https://github.com/nodejs/node/pull/3276", "description": "The `error` parameter can now be an arrow function." } ] }, "signatures": [ { "params": [ { "textRaw": "`fn` {Function}", "name": "fn", "type": "Function" }, { "textRaw": "`error` {RegExp|Function|Object|Error}", "name": "error", "type": "RegExp|Function|Object|Error", "optional": true }, { "textRaw": "`message` {string}", "name": "message", "type": "string", "optional": true } ] } ], "desc": "

Expects the function fn to throw an error.

\n

If specified, error can be a Class, RegExp, a validation function,\na validation object where each property will be tested for strict deep equality,\nor an instance of error where each property will be tested for strict deep\nequality including the non-enumerable message and name properties. When\nusing an object, it is also possible to use a regular expression, when\nvalidating against a string property. See below for examples.

\n

If specified, message will be appended to the message provided by the\nAssertionError if the fn call fails to throw or in case the error validation\nfails.

\n

Custom validation object/error instance:

\n
const err = new TypeError('Wrong value');\nerr.code = 404;\nerr.foo = 'bar';\nerr.info = {\n  nested: true,\n  baz: 'text'\n};\nerr.reg = /abc/i;\n\nassert.throws(\n  () => {\n    throw err;\n  },\n  {\n    name: 'TypeError',\n    message: 'Wrong value',\n    info: {\n      nested: true,\n      baz: 'text'\n    }\n    // Note that only properties on the validation object will be tested for.\n    // Using nested objects requires all properties to be present. Otherwise\n    // the validation is going to fail.\n  }\n);\n\n// Using regular expressions to validate error properties:\nassert.throws(\n  () => {\n    throw err;\n  },\n  {\n    // The `name` and `message` properties are strings and using regular\n    // expressions on those will match against the string. If they fail, an\n    // error is thrown.\n    name: /^TypeError$/,\n    message: /Wrong/,\n    foo: 'bar',\n    info: {\n      nested: true,\n      // It is not possible to use regular expressions for nested properties!\n      baz: 'text'\n    },\n    // The `reg` property contains a regular expression and only if the\n    // validation object contains an identical regular expression, it is going\n    // to pass.\n    reg: /abc/i\n  }\n);\n\n// Fails due to the different `message` and `name` properties:\nassert.throws(\n  () => {\n    const otherErr = new Error('Not found');\n    otherErr.code = 404;\n    throw otherErr;\n  },\n  err // This tests for `message`, `name` and `code`.\n);\n
\n

Validate instanceof using constructor:

\n
assert.throws(\n  () => {\n    throw new Error('Wrong value');\n  },\n  Error\n);\n
\n

Validate error message using RegExp:

\n

Using a regular expression runs .toString on the error object, and will\ntherefore also include the error name.

\n
assert.throws(\n  () => {\n    throw new Error('Wrong value');\n  },\n  /^Error: Wrong value$/\n);\n
\n

Custom error validation:

\n
assert.throws(\n  () => {\n    throw new Error('Wrong value');\n  },\n  function(err) {\n    if ((err instanceof Error) && /value/.test(err)) {\n      return true;\n    }\n  },\n  'unexpected error'\n);\n
\n

Note that error cannot be a string. If a string is provided as the second\nargument, then error is assumed to be omitted and the string will be used for\nmessage instead. This can lead to easy-to-miss mistakes. Using the same\nmessage as the thrown error message is going to result in an\nERR_AMBIGUOUS_ARGUMENT error. Please read the example below carefully if using\na string as the second argument gets considered:

\n\n
function throwingFirst() {\n  throw new Error('First');\n}\nfunction throwingSecond() {\n  throw new Error('Second');\n}\nfunction notThrowing() {}\n\n// The second argument is a string and the input function threw an Error.\n// The first case will not throw as it does not match for the error message\n// thrown by the input function!\nassert.throws(throwingFirst, 'Second');\n// In the next example the message has no benefit over the message from the\n// error and since it is not clear if the user intended to actually match\n// against the error message, Node.js thrown an `ERR_AMBIGUOUS_ARGUMENT` error.\nassert.throws(throwingSecond, 'Second');\n// Throws an error:\n// TypeError [ERR_AMBIGUOUS_ARGUMENT]\n\n// The string is only used (as message) in case the function does not throw:\nassert.throws(notThrowing, 'Second');\n// AssertionError [ERR_ASSERTION]: Missing expected exception: Second\n\n// If it was intended to match for the error message do this instead:\nassert.throws(throwingSecond, /Second$/);\n// Does not throw because the error messages match.\nassert.throws(throwingFirst, /Second$/);\n// Throws an error:\n// Error: First\n//     at throwingFirst (repl:2:9)\n
\n

Due to the confusing notation, it is recommended not to use a string as the\nsecond argument. This might lead to difficult-to-spot errors.

" } ], "type": "module", "displayName": "Assert" } ] }