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class="interior"> <header> <h1>Node.js v10.19.0 Documentation</h1> <div id="gtoc"> <ul> <li> <a href="index.html" name="toc">Index</a> </li> <li> <a href="all.html">View on single page</a> </li> <li> <a href="assert.json">View as JSON</a> </li> <li class="version-picker"> <a href="#">View another version <span>▼</span></a> <ol class="version-picker"><li><a href="https://nodejs.org/docs/latest-v12.x/api/assert.html">12.x</a></li> <li><a href="https://nodejs.org/docs/latest-v11.x/api/assert.html">11.x</a></li> <li><a href="https://nodejs.org/docs/latest-v10.x/api/assert.html">10.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v9.x/api/assert.html">9.x</a></li> <li><a href="https://nodejs.org/docs/latest-v8.x/api/assert.html">8.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v7.x/api/assert.html">7.x</a></li> <li><a href="https://nodejs.org/docs/latest-v6.x/api/assert.html">6.x</a></li> <li><a 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Contents</h2> <ul> <li><span class="stability_2"><a href="#assert_assert">Assert</a></span><ul> <li><a href="#assert_class_assert_assertionerror">Class: assert.AssertionError</a><ul> <li><a href="#assert_new_assert_assertionerror_options">new assert.AssertionError(options)</a></li> </ul> </li> <li><a href="#assert_strict_mode">Strict mode</a></li> <li><span class="stability_0"><a href="#assert_legacy_mode">Legacy mode</a></span></li> <li><a href="#assert_assert_value_message">assert(value[, message])</a></li> <li><a href="#assert_assert_deepequal_actual_expected_message">assert.deepEqual(actual, expected[, message])</a></li> <li><a href="#assert_assert_deepstrictequal_actual_expected_message">assert.deepStrictEqual(actual, expected[, message])</a><ul> <li><a href="#assert_comparison_details">Comparison details</a></li> </ul> </li> <li><a href="#assert_assert_doesnotreject_asyncfn_error_message">assert.doesNotReject(asyncFn[, error][, message])</a></li> <li><a href="#assert_assert_doesnotthrow_fn_error_message">assert.doesNotThrow(fn[, error][, message])</a></li> <li><a href="#assert_assert_equal_actual_expected_message">assert.equal(actual, expected[, message])</a></li> <li><a href="#assert_assert_fail_message">assert.fail([message])</a></li> <li><a href="#assert_assert_fail_actual_expected_message_operator_stackstartfn">assert.fail(actual, expected[, message[, operator[, stackStartFn]]])</a></li> <li><a href="#assert_assert_iferror_value">assert.ifError(value)</a></li> <li><a href="#assert_assert_notdeepequal_actual_expected_message">assert.notDeepEqual(actual, expected[, message])</a></li> <li><a href="#assert_assert_notdeepstrictequal_actual_expected_message">assert.notDeepStrictEqual(actual, expected[, message])</a></li> <li><a href="#assert_assert_notequal_actual_expected_message">assert.notEqual(actual, expected[, message])</a></li> <li><a href="#assert_assert_notstrictequal_actual_expected_message">assert.notStrictEqual(actual, expected[, message])</a></li> <li><a href="#assert_assert_ok_value_message">assert.ok(value[, message])</a></li> <li><a href="#assert_assert_rejects_asyncfn_error_message">assert.rejects(asyncFn[, error][, message])</a></li> <li><a href="#assert_assert_strictequal_actual_expected_message">assert.strictEqual(actual, expected[, message])</a></li> <li><a href="#assert_assert_throws_fn_error_message">assert.throws(fn[, error][, message])</a></li> </ul> </li> </ul> </div> <div id="apicontent"> <h1>Assert<span><a class="mark" href="#assert_assert" id="assert_assert">#</a></span></h1> <!--introduced_in=v0.1.21--> <div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p>The <code>assert</code> module provides a simple set of assertion tests that can be used to test invariants.</p> <p>A <code>strict</code> and a <code>legacy</code> mode exist, while it is recommended to only use <a href="#assert_strict_mode"><code>strict mode</code></a>.</p> <p>For more information about the used equality comparisons see <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness">MDN's guide on equality comparisons and sameness</a>.</p> <h2>Class: assert.AssertionError<span><a class="mark" href="#assert_class_assert_assertionerror" id="assert_class_assert_assertionerror">#</a></span></h2> <p>A subclass of <code>Error</code> that indicates the failure of an assertion. All errors thrown by the <code>assert</code> module will be instances of the <code>AssertionError</code> class.</p> <h3>new assert.AssertionError(options)<span><a class="mark" href="#assert_new_assert_assertionerror_options" id="assert_new_assert_assertionerror_options">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.1.21</span> </div><ul> <li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> If provided, the error message is going to be set to this value.</li> <li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The <code>actual</code> property on the error instance is going to contain this value. Internally used for the <code>actual</code> error input in case e.g., <a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a> is used.</li> <li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The <code>expected</code> property on the error instance is going to contain this value. Internally used for the <code>expected</code> error input in case e.g., <a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a> is used.</li> <li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The <code>operator</code> 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).</li> <li><code>stackStartFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> If provided, the generated stack trace is going to remove all frames up to the provided function.</li> </ul> </li> </ul> <p>A subclass of <code>Error</code> that indicates the failure of an assertion.</p> <p>All instances contain the built-in <code>Error</code> properties (<code>message</code> and <code>name</code>) and:</p> <ul> <li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Set to the actual value in case e.g., <a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a> is used.</li> <li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Set to the expected value in case e.g., <a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a> is used.</li> <li><code>generatedMessage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Indicates if the message was auto-generated (<code>true</code>) or not.</li> <li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> This is always set to the string <code>ERR_ASSERTION</code> to indicate that the error is actually an assertion error.</li> <li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Set to the passed in operator value.</li> </ul> <pre><code class="language-js">const assert = require('assert'); // Generate an AssertionError to compare the error message later: const { message } = new assert.AssertionError({ actual: 1, expected: 2, operator: 'strictEqual' }); // Verify error output: try { assert.strictEqual(1, 2); } catch (err) { assert(err instanceof assert.AssertionError); assert.strictEqual(err.message, message); assert.strictEqual(err.name, 'AssertionError [ERR_ASSERTION]'); assert.strictEqual(err.actual, 1); assert.strictEqual(err.expected, 2); assert.strictEqual(err.code, 'ERR_ASSERTION'); assert.strictEqual(err.operator, 'strictEqual'); assert.strictEqual(err.generatedMessage, true); }</code></pre> <h2>Strict mode<span><a class="mark" href="#assert_strict_mode" id="assert_strict_mode">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v9.9.0</td> <td><p>Added error diffs to the strict mode</p> </td></tr> <tr><td>v9.9.0</td> <td><p>Added strict mode to the assert module.</p> </td></tr> <tr><td>v9.9.0</td> <td><p><span>Added in: v9.9.0</span></p> </td></tr> </table> </details> </div><p>When using the <code>strict mode</code>, any <code>assert</code> function will use the equality used in the strict function mode. So <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a> will, for example, work the same as <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a>.</p> <p>On top of that, error messages which involve objects produce an error diff instead of displaying both objects. That is not the case for the legacy mode.</p> <p>It can be accessed using:</p> <pre><code class="language-js">const assert = require('assert').strict;</code></pre> <p>Example error diff:</p> <pre><code class="language-js">const assert = require('assert').strict; assert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]); // AssertionError: Input A expected to strictly deep-equal input B: // + expected - actual ... Lines skipped // // [ // [ // ... // 2, // - 3 // + '3' // ], // ... // 5 // ]</code></pre> <p>To deactivate the colors, use the <code>NODE_DISABLE_COLORS</code> environment variable. Please note that this will also deactivate the colors in the REPL.</p> <h2>Legacy mode<span><a class="mark" href="#assert_legacy_mode" id="assert_legacy_mode">#</a></span></h2> <div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use strict mode instead.</div><p>When accessing <code>assert</code> directly instead of using the <code>strict</code> property, the <a href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> will be used for any function without "strict" in its name, such as <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a>.</p> <p>It can be accessed using:</p> <pre><code class="language-js">const assert = require('assert');</code></pre> <p>It is recommended to use the <a href="#assert_strict_mode"><code>strict mode</code></a> instead as the <a href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> can often have surprising results. This is especially true for <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a>, where the comparison rules are lax:</p> <pre><code class="language-js">// WARNING: This does not throw an AssertionError! assert.deepEqual(/a/gi, new Date());</code></pre> <h2>assert(value[, message])<span><a class="mark" href="#assert_assert_value_message" id="assert_assert_value_message">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.5.9</span> </div><ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The input that is checked for being truthy.</li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> </ul> <p>An alias of <a href="#assert_assert_ok_value_message"><code>assert.ok()</code></a>.</p> <h2>assert.deepEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_deepequal_actual_expected_message" id="assert_assert_deepequal_actual_expected_message">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v9.0.0</td> <td><p>The <code>Error</code> names and messages are now properly compared</p> </td></tr> <tr><td>v8.0.0</td> <td><p>The <code>Set</code> and <code>Map</code> content is also compared</p> </td></tr> <tr><td>v6.4.0, v4.7.1</td> <td><p>Typed array slices are handled correctly now.</p> </td></tr> <tr><td>v6.1.0, v4.5.0</td> <td><p>Objects with circular references can be used as inputs now.</p> </td></tr> <tr><td>v5.10.1, v4.4.3</td> <td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p> </td></tr> <tr><td>v0.1.21</td> <td><p><span>Added in: v0.1.21</span></p> </td></tr> </table> </details> </div><ul> <li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> </ul> <p><strong>Strict mode</strong></p> <p>An alias of <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a>.</p> <p><strong>Legacy mode</strong></p> <div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use [`assert.deepStrictEqual()`][] instead.</div><p>Tests for deep equality between the <code>actual</code> and <code>expected</code> parameters. Primitive values are compared with the <a href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> ( <code>==</code> ).</p> <p>Only <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties">enumerable "own" properties</a> are considered. The <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a> implementation does not test the <a href="https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots"><code>[[Prototype]]</code></a> of objects or enumerable own <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol"><code>Symbol</code></a> properties. For such checks, consider using <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a> instead. <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a> can have potentially surprising results. The following example does not throw an <code>AssertionError</code> because the properties on the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a> object are not enumerable:</p> <pre><code class="language-js">// WARNING: This does not throw an AssertionError! assert.deepEqual(/a/gi, new Date());</code></pre> <p>An exception is made for <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a>. <code>Map</code>s and <code>Set</code>s have their contained items compared too, as expected.</p> <p>"Deep" equality means that the enumerable "own" properties of child objects are evaluated also:</p> <pre><code class="language-js">const assert = require('assert'); const obj1 = { a: { b: 1 } }; const obj2 = { a: { b: 2 } }; const obj3 = { a: { b: 1 } }; const obj4 = Object.create(obj1); assert.deepEqual(obj1, obj1); // OK // Values of b are different: assert.deepEqual(obj1, obj2); // AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } } assert.deepEqual(obj1, obj3); // OK // Prototypes are ignored: assert.deepEqual(obj1, obj4); // AssertionError: { a: { b: 1 } } deepEqual {}</code></pre> <p>If the values are not equal, an <code>AssertionError</code> is thrown with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If the <code>message</code> parameter is undefined, a default error message is assigned. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the <code>AssertionError</code>.</p> <h2>assert.deepStrictEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_deepstrictequal_actual_expected_message" id="assert_assert_deepstrictequal_actual_expected_message">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v9.0.0</td> <td><p>Enumerable symbol properties are now compared.</p> </td></tr> <tr><td>v9.0.0</td> <td><p>The <code>NaN</code> is now compared using the <a href="https://tc39.github.io/ecma262/#sec-samevaluezero">SameValueZero</a> comparison.</p> </td></tr> <tr><td>v8.5.0</td> <td><p>The <code>Error</code> names and messages are now properly compared</p> </td></tr> <tr><td>v8.0.0</td> <td><p>The <code>Set</code> and <code>Map</code> content is also compared</p> </td></tr> <tr><td>v6.4.0, v4.7.1</td> <td><p>Typed array slices are handled correctly now.</p> </td></tr> <tr><td>v6.1.0</td> <td><p>Objects with circular references can be used as inputs now.</p> </td></tr> <tr><td>v5.10.1, v4.4.3</td> <td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p> </td></tr> <tr><td>v1.2.0</td> <td><p><span>Added in: v1.2.0</span></p> </td></tr> </table> </details> </div><ul> <li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> </ul> <p>Tests for deep equality between the <code>actual</code> and <code>expected</code> parameters. "Deep" equality means that the enumerable "own" properties of child objects are recursively evaluated also by the following rules.</p> <h3>Comparison details<span><a class="mark" href="#assert_comparison_details" id="assert_comparison_details">#</a></span></h3> <ul> <li>Primitive values are compared using the <a href="https://tc39.github.io/ecma262/#sec-samevalue">SameValue Comparison</a>, used by <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is"><code>Object.is()</code></a>.</li> <li><a href="https://tc39.github.io/ecma262/#sec-object.prototype.tostring">Type tags</a> of objects should be the same.</li> <li><a href="https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots"><code>[[Prototype]]</code></a> of objects are compared using the <a href="https://tc39.github.io/ecma262/#sec-strict-equality-comparison">Strict Equality Comparison</a>.</li> <li>Only <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties">enumerable "own" properties</a> are considered.</li> <li><a href="errors.html#errors_class_error"><code>Error</code></a> names and messages are always compared, even if these are not enumerable properties.</li> <li>Enumerable own <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol"><code>Symbol</code></a> properties are compared as well.</li> <li><a href="https://developer.mozilla.org/en-US/docs/Glossary/Primitive#Primitive_wrapper_objects_in_JavaScript">Object wrappers</a> are compared both as objects and unwrapped values.</li> <li><code>Object</code> properties are compared unordered.</li> <li><code>Map</code> keys and <code>Set</code> items are compared unordered.</li> <li>Recursion stops when both sides differ or both sides encounter a circular reference.</li> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> comparison does not rely on their values. See below for further details.</li> </ul> <pre><code class="language-js">const assert = require('assert').strict; // This fails because 1 !== '1'. assert.deepStrictEqual({ a: 1 }, { a: '1' }); // AssertionError: Input A expected to strictly deep-equal input B: // + expected - actual // { // - a: 1 // + a: '1' // } // The following objects don't have own properties const date = new Date(); const object = {}; const fakeDate = {}; Object.setPrototypeOf(fakeDate, Date.prototype); // Different [[Prototype]]: assert.deepStrictEqual(object, fakeDate); // AssertionError: Input A expected to strictly deep-equal input B: // + expected - actual // - {} // + Date {} // Different type tags: assert.deepStrictEqual(date, fakeDate); // AssertionError: Input A expected to strictly deep-equal input B: // + expected - actual // - 2018-04-26T00:49:08.604Z // + Date {} assert.deepStrictEqual(NaN, NaN); // OK, because of the SameValue comparison // Different unwrapped numbers: assert.deepStrictEqual(new Number(1), new Number(2)); // AssertionError: Input A expected to strictly deep-equal input B: // + expected - actual // - [Number: 1] // + [Number: 2] assert.deepStrictEqual(new String('foo'), Object('foo')); // OK because the object and the string are identical when unwrapped. assert.deepStrictEqual(-0, -0); // OK // Different zeros using the SameValue Comparison: assert.deepStrictEqual(0, -0); // AssertionError: Input A expected to strictly deep-equal input B: // + expected - actual // - 0 // + -0 const symbol1 = Symbol(); const symbol2 = Symbol(); assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol1]: 1 }); // OK, because it is the same symbol on both objects. assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 }); // AssertionError [ERR_ASSERTION]: Input objects not identical: // { // [Symbol()]: 1 // } const weakMap1 = new WeakMap(); const weakMap2 = new WeakMap([[{}, {}]]); const weakMap3 = new WeakMap(); weakMap3.unequal = true; assert.deepStrictEqual(weakMap1, weakMap2); // OK, because it is impossible to compare the entries // Fails because weakMap3 has a property that weakMap1 does not contain: assert.deepStrictEqual(weakMap1, weakMap3); // AssertionError: Input A expected to strictly deep-equal input B: // + expected - actual // WeakMap { // - [items unknown] // + [items unknown], // + unequal: true // }</code></pre> <p>If the values are not equal, an <code>AssertionError</code> is thrown with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If the <code>message</code> parameter is undefined, a default error message is assigned. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the <code>AssertionError</code>.</p> <h2>assert.doesNotReject(asyncFn[, error][, message])<span><a class="mark" href="#assert_assert_doesnotreject_asyncfn_error_message" id="assert_assert_doesnotreject_asyncfn_error_message">#</a></span></h2> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div><ul> <li><code>asyncFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a></li> <li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>Awaits the <code>asyncFn</code> promise or, if <code>asyncFn</code> is a function, immediately calls the function and awaits the returned promise to complete. It will then check that the promise is not rejected.</p> <p>If <code>asyncFn</code> is a function and it throws an error synchronously, <code>assert.doesNotReject()</code> will return a rejected <code>Promise</code> with that error. If the function does not return a promise, <code>assert.doesNotReject()</code> will return a rejected <code>Promise</code> with an <a href="errors.html#errors_err_invalid_return_value"><code>ERR_INVALID_RETURN_VALUE</code></a> error. In both cases the error handler is skipped.</p> <p>Using <code>assert.doesNotReject()</code> is actually not useful because there is little benefit in catching a rejection and then rejecting it again. Instead, consider adding a comment next to the specific code path that should not reject and keep error messages as expressive as possible.</p> <p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a> or a validation function. See <a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a> for more details.</p> <p>Besides the async nature to await the completion behaves identically to <a href="#assert_assert_doesnotthrow_fn_error_message"><code>assert.doesNotThrow()</code></a>.</p> <pre><code class="language-js">(async () => { await assert.doesNotReject( async () => { throw new TypeError('Wrong value'); }, SyntaxError ); })();</code></pre> <pre><code class="language-js">assert.doesNotReject(Promise.reject(new TypeError('Wrong value'))) .then(() => { // ... });</code></pre> <h2>assert.doesNotThrow(fn[, error][, message])<span><a class="mark" href="#assert_assert_doesnotthrow_fn_error_message" id="assert_assert_doesnotthrow_fn_error_message">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v5.11.0, v4.4.5</td> <td><p>The <code>message</code> parameter is respected now.</p> </td></tr> <tr><td>v4.2.0</td> <td><p>The <code>error</code> parameter can now be an arrow function.</p> </td></tr> <tr><td>v0.1.21</td> <td><p><span>Added in: v0.1.21</span></p> </td></tr> </table> </details> </div><ul> <li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> <li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>Asserts that the function <code>fn</code> does not throw an error.</p> <p>Using <code>assert.doesNotThrow()</code> is actually not useful because there is no benefit in catching an error and then rethrowing it. Instead, consider adding a comment next to the specific code path that should not throw and keep error messages as expressive as possible.</p> <p>When <code>assert.doesNotThrow()</code> is called, it will immediately call the <code>fn</code> function.</p> <p>If an error is thrown and it is the same type as that specified by the <code>error</code> parameter, then an <code>AssertionError</code> is thrown. If the error is of a different type, or if the <code>error</code> parameter is undefined, the error is propagated back to the caller.</p> <p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a> or a validation function. See <a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a> for more details.</p> <p>The following, for instance, will throw the <a href="errors.html#errors_class_typeerror"><code>TypeError</code></a> because there is no matching error type in the assertion:</p> <!-- eslint-disable no-restricted-syntax --> <pre><code class="language-js">assert.doesNotThrow( () => { throw new TypeError('Wrong value'); }, SyntaxError );</code></pre> <p>However, the following will result in an <code>AssertionError</code> with the message 'Got unwanted exception...':</p> <!-- eslint-disable no-restricted-syntax --> <pre><code class="language-js">assert.doesNotThrow( () => { throw new TypeError('Wrong value'); }, TypeError );</code></pre> <p>If an <code>AssertionError</code> is thrown and a value is provided for the <code>message</code> parameter, the value of <code>message</code> will be appended to the <code>AssertionError</code> message:</p> <!-- eslint-disable no-restricted-syntax --> <pre><code class="language-js">assert.doesNotThrow( () => { throw new TypeError('Wrong value'); }, /Wrong value/, 'Whoops' ); // Throws: AssertionError: Got unwanted exception: Whoops</code></pre> <h2>assert.equal(actual, expected[, message])<span><a class="mark" href="#assert_assert_equal_actual_expected_message" id="assert_assert_equal_actual_expected_message">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.1.21</span> </div><ul> <li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> </ul> <p><strong>Strict mode</strong></p> <p>An alias of <a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a>.</p> <p><strong>Legacy mode</strong></p> <div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use [`assert.strictEqual()`][] instead.</div><p>Tests shallow, coercive equality between the <code>actual</code> and <code>expected</code> parameters using the <a href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> ( <code>==</code> ).</p> <pre><code class="language-js">const assert = require('assert'); assert.equal(1, 1); // OK, 1 == 1 assert.equal(1, '1'); // OK, 1 == '1' assert.equal(1, 2); // AssertionError: 1 == 2 assert.equal({ a: { b: 1 } }, { a: { b: 1 } }); // AssertionError: { a: { b: 1 } } == { a: { b: 1 } }</code></pre> <p>If the values are not equal, an <code>AssertionError</code> is thrown with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If the <code>message</code> parameter is undefined, a default error message is assigned. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the <code>AssertionError</code>.</p> <h2>assert.fail([message])<span><a class="mark" href="#assert_assert_fail_message" id="assert_assert_fail_message">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.1.21</span> </div><ul> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a> <strong>Default:</strong> <code>'Failed'</code></li> </ul> <p>Throws an <code>AssertionError</code> with the provided error message or a default error message. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the <code>AssertionError</code>.</p> <pre><code class="language-js">const assert = require('assert').strict; assert.fail(); // AssertionError [ERR_ASSERTION]: Failed assert.fail('boom'); // AssertionError [ERR_ASSERTION]: boom assert.fail(new TypeError('need array')); // TypeError: need array</code></pre> <p>Using <code>assert.fail()</code> with more than two arguments is possible but deprecated. See below for further details.</p> <h2>assert.fail(actual, expected[, message[, operator[, stackStartFn]]])<span><a class="mark" href="#assert_assert_fail_actual_expected_message_operator_stackstartfn" id="assert_assert_fail_actual_expected_message_operator_stackstartfn">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v10.0.0</td> <td><p>Calling <code>assert.fail()</code> with more than one argument is deprecated and emits a warning.</p> </td></tr> <tr><td>v0.1.21</td> <td><p><span>Added in: v0.1.21</span></p> </td></tr> </table> </details> </div><ul> <li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> <li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> <strong>Default:</strong> <code>'!='</code></li> <li><code>stackStartFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> <strong>Default:</strong> <code>assert.fail</code></li> </ul> <div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use `assert.fail([message])` or other assert functions instead.</div><p>If <code>message</code> is falsy, the error message is set as the values of <code>actual</code> and <code>expected</code> separated by the provided <code>operator</code>. If just the two <code>actual</code> and <code>expected</code> arguments are provided, <code>operator</code> will default to <code>'!='</code>. If <code>message</code> is provided as third argument it will be used as the error message and the other arguments will be stored as properties on the thrown object. If <code>stackStartFn</code> is provided, all stack frames above that function will be removed from stacktrace (see <a href="errors.html#errors_error_capturestacktrace_targetobject_constructoropt"><code>Error.captureStackTrace</code></a>). If no arguments are given, the default message <code>Failed</code> will be used.</p> <pre><code class="language-js">const assert = require('assert').strict; assert.fail('a', 'b'); // AssertionError [ERR_ASSERTION]: 'a' != 'b' assert.fail(1, 2, undefined, '>'); // AssertionError [ERR_ASSERTION]: 1 > 2 assert.fail(1, 2, 'fail'); // AssertionError [ERR_ASSERTION]: fail assert.fail(1, 2, 'whoops', '>'); // AssertionError [ERR_ASSERTION]: whoops assert.fail(1, 2, new TypeError('need array')); // TypeError: need array</code></pre> <p>In the last three cases <code>actual</code>, <code>expected</code>, and <code>operator</code> have no influence on the error message.</p> <p>Example use of <code>stackStartFn</code> for truncating the exception's stacktrace:</p> <pre><code class="language-js">function suppressFrame() { assert.fail('a', 'b', undefined, '!==', suppressFrame); } suppressFrame(); // AssertionError [ERR_ASSERTION]: 'a' !== 'b' // at repl:1:1 // at ContextifyScript.Script.runInThisContext (vm.js:44:33) // ...</code></pre> <h2>assert.ifError(value)<span><a class="mark" href="#assert_assert_iferror_value" id="assert_assert_iferror_value">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v10.0.0</td> <td><p>Instead of throwing the original error it is now wrapped into an <code>AssertionError</code> that contains the full stack trace.</p> </td></tr> <tr><td>v10.0.0</td> <td><p>Value may now only be <code>undefined</code> or <code>null</code>. Before all falsy values were handled the same as <code>null</code> and did not throw.</p> </td></tr> <tr><td>v0.1.97</td> <td><p><span>Added in: v0.1.97</span></p> </td></tr> </table> </details> </div><ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> </ul> <p>Throws <code>value</code> if <code>value</code> is not <code>undefined</code> or <code>null</code>. This is useful when testing the <code>error</code> argument in callbacks. The stack trace contains all frames from the error passed to <code>ifError()</code> including the potential new frames for <code>ifError()</code> itself.</p> <pre><code class="language-js">const assert = require('assert').strict; assert.ifError(null); // OK assert.ifError(0); // AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0 assert.ifError('error'); // AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error' assert.ifError(new Error()); // AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error // Create some random error frames. let err; (function errorFrame() { err = new Error('test error'); })(); (function ifErrorFrame() { assert.ifError(err); })(); // AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error // at ifErrorFrame // at errorFrame</code></pre> <h2>assert.notDeepEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_notdeepequal_actual_expected_message" id="assert_assert_notdeepequal_actual_expected_message">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v9.0.0</td> <td><p>The <code>Error</code> names and messages are now properly compared</p> </td></tr> <tr><td>v8.0.0</td> <td><p>The <code>Set</code> and <code>Map</code> content is also compared</p> </td></tr> <tr><td>v6.4.0, v4.7.1</td> <td><p>Typed array slices are handled correctly now.</p> </td></tr> <tr><td>v6.1.0, v4.5.0</td> <td><p>Objects with circular references can be used as inputs now.</p> </td></tr> <tr><td>v5.10.1, v4.4.3</td> <td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p> </td></tr> <tr><td>v0.1.21</td> <td><p><span>Added in: v0.1.21</span></p> </td></tr> </table> </details> </div><ul> <li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> </ul> <p><strong>Strict mode</strong></p> <p>An alias of <a href="#assert_assert_notdeepstrictequal_actual_expected_message"><code>assert.notDeepStrictEqual()</code></a>.</p> <p><strong>Legacy mode</strong></p> <div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use [`assert.notDeepStrictEqual()`][] instead.</div><p>Tests for any deep inequality. Opposite of <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a>.</p> <pre><code class="language-js">const assert = require('assert'); const obj1 = { a: { b: 1 } }; const obj2 = { a: { b: 2 } }; const obj3 = { a: { b: 1 } }; const obj4 = Object.create(obj1); assert.notDeepEqual(obj1, obj1); // AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } } assert.notDeepEqual(obj1, obj2); // OK assert.notDeepEqual(obj1, obj3); // AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } } assert.notDeepEqual(obj1, obj4); // OK</code></pre> <p>If the values are deeply equal, an <code>AssertionError</code> is thrown with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If the <code>message</code> parameter is undefined, a default error message is assigned. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the <code>AssertionError</code>.</p> <h2>assert.notDeepStrictEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_notdeepstrictequal_actual_expected_message" id="assert_assert_notdeepstrictequal_actual_expected_message">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v9.0.0</td> <td><p>The <code>-0</code> and <code>+0</code> are not considered equal anymore.</p> </td></tr> <tr><td>v9.0.0</td> <td><p>The <code>NaN</code> is now compared using the <a href="https://tc39.github.io/ecma262/#sec-samevaluezero">SameValueZero</a> comparison.</p> </td></tr> <tr><td>v9.0.0</td> <td><p>The <code>Error</code> names and messages are now properly compared</p> </td></tr> <tr><td>v8.0.0</td> <td><p>The <code>Set</code> and <code>Map</code> content is also compared</p> </td></tr> <tr><td>v6.4.0, v4.7.1</td> <td><p>Typed array slices are handled correctly now.</p> </td></tr> <tr><td>v6.1.0</td> <td><p>Objects with circular references can be used as inputs now.</p> </td></tr> <tr><td>v5.10.1, v4.4.3</td> <td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p> </td></tr> <tr><td>v1.2.0</td> <td><p><span>Added in: v1.2.0</span></p> </td></tr> </table> </details> </div><ul> <li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> </ul> <p>Tests for deep strict inequality. Opposite of <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a>.</p> <pre><code class="language-js">const assert = require('assert').strict; assert.notDeepStrictEqual({ a: 1 }, { a: '1' }); // OK</code></pre> <p>If the values are deeply and strictly equal, an <code>AssertionError</code> is thrown with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If the <code>message</code> parameter is undefined, a default error message is assigned. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the <code>AssertionError</code>.</p> <h2>assert.notEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_notequal_actual_expected_message" id="assert_assert_notequal_actual_expected_message">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.1.21</span> </div><ul> <li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> </ul> <p><strong>Strict mode</strong></p> <p>An alias of <a href="#assert_assert_notstrictequal_actual_expected_message"><code>assert.notStrictEqual()</code></a>.</p> <p><strong>Legacy mode</strong></p> <div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use [`assert.notStrictEqual()`][] instead.</div><p>Tests shallow, coercive inequality with the <a href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> ( <code>!=</code> ).</p> <pre><code class="language-js">const assert = require('assert'); assert.notEqual(1, 2); // OK assert.notEqual(1, 1); // AssertionError: 1 != 1 assert.notEqual(1, '1'); // AssertionError: 1 != '1'</code></pre> <p>If the values are equal, an <code>AssertionError</code> is thrown with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If the <code>message</code> parameter is undefined, a default error message is assigned. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the <code>AssertionError</code>.</p> <h2>assert.notStrictEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_notstrictequal_actual_expected_message" id="assert_assert_notstrictequal_actual_expected_message">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v10.0.0</td> <td><p>Used comparison changed from Strict Equality to <code>Object.is()</code></p> </td></tr> <tr><td>v0.1.21</td> <td><p><span>Added in: v0.1.21</span></p> </td></tr> </table> </details> </div><ul> <li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> </ul> <p>Tests strict inequality between the <code>actual</code> and <code>expected</code> parameters as determined by the <a href="https://tc39.github.io/ecma262/#sec-samevalue">SameValue Comparison</a>.</p> <pre><code class="language-js">const assert = require('assert').strict; assert.notStrictEqual(1, 2); // OK assert.notStrictEqual(1, 1); // AssertionError [ERR_ASSERTION]: Identical input passed to notStrictEqual: 1 assert.notStrictEqual(1, '1'); // OK</code></pre> <p>If the values are strictly equal, an <code>AssertionError</code> is thrown with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If the <code>message</code> parameter is undefined, a default error message is assigned. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the <code>AssertionError</code>.</p> <h2>assert.ok(value[, message])<span><a class="mark" href="#assert_assert_ok_value_message" id="assert_assert_ok_value_message">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v10.0.0</td> <td><p>The <code>assert.ok()</code> (no arguments) will now use a predefined error message.</p> </td></tr> <tr><td>v0.1.21</td> <td><p><span>Added in: v0.1.21</span></p> </td></tr> </table> </details> </div><ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> </ul> <p>Tests if <code>value</code> is truthy. It is equivalent to <code>assert.equal(!!value, true, message)</code>.</p> <p>If <code>value</code> is not truthy, an <code>AssertionError</code> is thrown with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If the <code>message</code> parameter is <code>undefined</code>, a default error message is assigned. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the <code>AssertionError</code>. If no arguments are passed in at all <code>message</code> will be set to the string: <code>'No value argument passed to `assert.ok()`'</code>.</p> <p>Be aware that in the <code>repl</code> the error message will be different to the one thrown in a file! See below for further details.</p> <pre><code class="language-js">const assert = require('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) // Using `assert()` works the same: assert(0); // AssertionError: The expression evaluated to a falsy value: // // assert(0)</code></pre> <h2>assert.rejects(asyncFn[, error][, message])<span><a class="mark" href="#assert_assert_rejects_asyncfn_error_message" id="assert_assert_rejects_asyncfn_error_message">#</a></span></h2> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div><ul> <li><code>asyncFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a></li> <li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>Awaits the <code>asyncFn</code> promise or, if <code>asyncFn</code> is a function, immediately calls the function and awaits the returned promise to complete. It will then check that the promise is rejected.</p> <p>If <code>asyncFn</code> is a function and it throws an error synchronously, <code>assert.rejects()</code> will return a rejected <code>Promise</code> with that error. If the function does not return a promise, <code>assert.rejects()</code> will return a rejected <code>Promise</code> with an <a href="errors.html#errors_err_invalid_return_value"><code>ERR_INVALID_RETURN_VALUE</code></a> error. In both cases the error handler is skipped.</p> <p>Besides the async nature to await the completion behaves identically to <a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a>.</p> <p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>, a validation function, an object where each property will be tested for, or an instance of error where each property will be tested for including the non-enumerable <code>message</code> and <code>name</code> properties.</p> <p>If specified, <code>message</code> will be the message provided by the <code>AssertionError</code> if the <code>asyncFn</code> fails to reject.</p> <pre><code class="language-js">(async () => { await assert.rejects( async () => { throw new TypeError('Wrong value'); }, { name: 'TypeError', message: 'Wrong value' } ); })();</code></pre> <pre><code class="language-js">assert.rejects( Promise.reject(new Error('Wrong value')), Error ).then(() => { // ... });</code></pre> <p>Note that <code>error</code> cannot be a string. If a string is provided as the second argument, then <code>error</code> is assumed to be omitted and the string will be used for <code>message</code> instead. This can lead to easy-to-miss mistakes. Please read the example in <a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a> carefully if using a string as the second argument gets considered.</p> <h2>assert.strictEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_strictequal_actual_expected_message" id="assert_assert_strictequal_actual_expected_message">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v10.0.0</td> <td><p>Used comparison changed from Strict Equality to <code>Object.is()</code></p> </td></tr> <tr><td>v0.1.21</td> <td><p><span>Added in: v0.1.21</span></p> </td></tr> </table> </details> </div><ul> <li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> </ul> <p>Tests strict equality between the <code>actual</code> and <code>expected</code> parameters as determined by the <a href="https://tc39.github.io/ecma262/#sec-samevalue">SameValue Comparison</a>.</p> <pre><code class="language-js">const assert = require('assert').strict; assert.strictEqual(1, 2); // AssertionError [ERR_ASSERTION]: Input A expected to strictly equal input B: // + expected - actual // - 1 // + 2 assert.strictEqual(1, 1); // OK assert.strictEqual(1, '1'); // AssertionError [ERR_ASSERTION]: Input A expected to strictly equal input B: // + expected - actual // - 1 // + '1'</code></pre> <p>If the values are not strictly equal, an <code>AssertionError</code> is thrown with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If the <code>message</code> parameter is undefined, a default error message is assigned. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the <code>AssertionError</code>.</p> <h2>assert.throws(fn[, error][, message])<span><a class="mark" href="#assert_assert_throws_fn_error_message" id="assert_assert_throws_fn_error_message">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v10.2.0</td> <td><p>The <code>error</code> parameter can be an object containing regular expressions now.</p> </td></tr> <tr><td>v9.9.0</td> <td><p>The <code>error</code> parameter can now be an object as well.</p> </td></tr> <tr><td>v4.2.0</td> <td><p>The <code>error</code> parameter can now be an arrow function.</p> </td></tr> <tr><td>v0.1.21</td> <td><p><span>Added in: v0.1.21</span></p> </td></tr> </table> </details> </div><ul> <li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> <li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>Expects the function <code>fn</code> to throw an error.</p> <p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>, a validation function, a validation object where each property will be tested for strict deep equality, or an instance of error where each property will be tested for strict deep equality including the non-enumerable <code>message</code> and <code>name</code> properties. When using an object, it is also possible to use a regular expression, when validating against a string property. See below for examples.</p> <p>If specified, <code>message</code> will be appended to the message provided by the <code>AssertionError</code> if the <code>fn</code> call fails to throw or in case the error validation fails.</p> <p>Custom validation object/error instance:</p> <pre><code class="language-js">const err = new TypeError('Wrong value'); err.code = 404; err.foo = 'bar'; err.info = { nested: true, baz: 'text' }; err.reg = /abc/i; assert.throws( () => { throw err; }, { name: 'TypeError', message: 'Wrong value', info: { nested: true, baz: 'text' } // Note that only properties on the validation object will be tested for. // Using nested objects requires all properties to be present. Otherwise // the validation is going to fail. } ); // Using regular expressions to validate error properties: assert.throws( () => { throw err; }, { // The `name` and `message` properties are strings and using regular // expressions on those will match against the string. If they fail, an // error is thrown. name: /^TypeError$/, message: /Wrong/, foo: 'bar', info: { nested: true, // It is not possible to use regular expressions for nested properties! baz: 'text' }, // The `reg` property contains a regular expression and only if the // validation object contains an identical regular expression, it is going // to pass. reg: /abc/i } ); // Fails due to the different `message` and `name` properties: assert.throws( () => { const otherErr = new Error('Not found'); otherErr.code = 404; throw otherErr; }, err // This tests for `message`, `name` and `code`. );</code></pre> <p>Validate instanceof using constructor:</p> <pre><code class="language-js">assert.throws( () => { throw new Error('Wrong value'); }, Error );</code></pre> <p>Validate error message using <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>:</p> <p>Using a regular expression runs <code>.toString</code> on the error object, and will therefore also include the error name.</p> <pre><code class="language-js">assert.throws( () => { throw new Error('Wrong value'); }, /^Error: Wrong value$/ );</code></pre> <p>Custom error validation:</p> <pre><code class="language-js">assert.throws( () => { throw new Error('Wrong value'); }, function(err) { if ((err instanceof Error) && /value/.test(err)) { return true; } }, 'unexpected error' );</code></pre> <p>Note that <code>error</code> cannot be a string. If a string is provided as the second argument, then <code>error</code> is assumed to be omitted and the string will be used for <code>message</code> instead. This can lead to easy-to-miss mistakes. Using the same message as the thrown error message is going to result in an <code>ERR_AMBIGUOUS_ARGUMENT</code> error. Please read the example below carefully if using a string as the second argument gets considered:</p> <!-- eslint-disable no-restricted-syntax --> <pre><code class="language-js">function throwingFirst() { throw new Error('First'); } function throwingSecond() { throw new Error('Second'); } function notThrowing() {} // The second argument is a string and the input function threw an Error. // The first case will not throw as it does not match for the error message // thrown by the input function! assert.throws(throwingFirst, 'Second'); // In the next example the message has no benefit over the message from the // error and since it is not clear if the user intended to actually match // against the error message, Node.js thrown an `ERR_AMBIGUOUS_ARGUMENT` error. assert.throws(throwingSecond, 'Second'); // Throws an error: // TypeError [ERR_AMBIGUOUS_ARGUMENT] // The string is only used (as message) in case the function does not throw: assert.throws(notThrowing, 'Second'); // AssertionError [ERR_ASSERTION]: Missing expected exception: Second // If it was intended to match for the error message do this instead: assert.throws(throwingSecond, /Second$/); // Does not throw because the error messages match. assert.throws(throwingFirst, /Second$/); // Throws an error: // Error: First // at throwingFirst (repl:2:9)</code></pre> <p>Due to the confusing notation, it is recommended not to use a string as the second argument. This might lead to difficult-to-spot errors.</p> </div> </div> </div> <script src="assets/sh_main.js"></script> <script src="assets/sh_javascript.min.js"></script> <script>highlight(undefined, undefined, 'pre');</script> </body> </html>
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