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+---
+title: Logical NOT (!)
+slug: Web/JavaScript/Reference/Operators/Logical_NOT
+translation_of: Web/JavaScript/Reference/Operators/Logical_NOT
+---
+<div>{{jsSidebar("Operators")}}</div>
+
+<p>The logical NOT (<code>!</code>) operator (logical complement, negation) takes truth to falsity and vice versa. It is typically used with {{jsxref("Boolean")}} (logical) values. When used with non-Boolean values, it returns <code>false</code> if its single operand can be converted to <code>true</code>; otherwise, returns <code>true</code>.</p>
+
+<div>{{EmbedInteractiveExample("pages/js/expressions-logical-not.html", "shorter")}}</div>
+
+<div class="hidden">The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone <a href="https://github.com/mdn/interactive-examples">https://github.com/mdn/interactive-examples</a> and send us a pull request.</div>
+
+<h2 id="语法">语法</h2>
+
+<pre class="syntaxbox notranslate">!<var>expr</var>
+</pre>
+
+<h2 id="Description">Description</h2>
+
+<p>Returns <code>false</code> if its single operand can be converted to <code>true</code>; otherwise, returns <code>true</code>.</p>
+
+<p>If a value can be converted to <code>true</code>, the value is so-called {{Glossary("truthy")}}. If a value can be converted to <code>false</code>, the value is so-called {{Glossary("falsy")}}.</p>
+
+<p>Examples of expressions that can be converted to false are:</p>
+
+<ul>
+ <li><code>null</code>;</li>
+ <li><code>NaN</code>;</li>
+ <li><code>0</code>;</li>
+ <li>empty string (<code>""</code> or <code>''</code> or <code>``</code>);</li>
+ <li><code>undefined</code>.</li>
+</ul>
+
+<p>Even though the <code>!</code> operator can be used with operands that are not Boolean values, it can still be considered a boolean operator since its return value can always be converted to a <a href="/en-US/docs/Web/JavaScript/Data_structures#Boolean_type">boolean primitive</a>. To explicitly convert its return value (or any expression in general) to the corresponding boolean value, use a double <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators#Logical_NOT">NOT operator</a> or the {{jsxref("Global_Objects/Boolean/Boolean", "Boolean")}} constructor.</p>
+
+<h2 id="Examples">Examples</h2>
+
+<h3 id="Using_NOT">Using NOT</h3>
+
+<p>The following code shows examples of the <code>!</code> (logical NOT) operator.</p>
+
+<pre class="brush: js notranslate">n1 = !true               // !t returns false
+n2 = !false              // !f returns true
+n3 = !''                 // !f returns true
+n4 = !'Cat'              // !t returns false</pre>
+
+<h3 id="Double_NOT_!!">Double NOT (<code>!!</code>)</h3>
+
+<p>It is possible to use a couple of NOT operators in series to explicitly force the conversion of any value to the corresponding <a href="/en-US/docs/Web/JavaScript/Data_structures#Boolean_type">boolean primitive</a>. The conversion is based on the "truthyness" or "falsyness" of the value (see {{Glossary("truthy")}} and {{Glossary("falsy")}}).</p>
+
+<p>The same conversion can be done through the {{jsxref("Global_Objects/Boolean/Boolean", "Boolean")}} function.</p>
+
+<pre class="brush: js notranslate">n1 = !!true                   // !!truthy returns true
+n2 = !!{}                     // !!truthy returns true: <strong>any</strong> object is truthy...
+n3 = !!(new Boolean(false))   // ...even Boolean objects with a false <em>.valueOf()</em>!
+n4 = !!false                  // !!falsy returns false
+n5 = !!""                     // !!falsy returns false
+n6 = !!Boolean(false)         // !!falsy returns false</pre>
+
+<h3 id="Converting_between_NOTs">Converting between NOTs</h3>
+
+<p>The following operation involving <strong>booleans</strong>:</p>
+
+<pre class="brush: js notranslate">!!bCondition</pre>
+
+<p>is always equal to:</p>
+
+<pre class="brush: js notranslate">bCondition</pre>
+
+<h2 id="Specifications">Specifications</h2>
+
+<table class="standard-table">
+ <thead>
+  <tr>
+   <th scope="col">Specification</th>
+  </tr>
+ </thead>
+ <tbody>
+  <tr>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#sec-logical-not-operator', 'Logical NOT expression')}}</td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="Browser_compatibility">Browser compatibility</h2>
+
+
+
+<p>{{Compat("javascript.operators.logical_not")}}</p>
+
+<h2 id="See_also">See also</h2>
+
+<ul>
+ <li>{{jsxref("Boolean")}}</li>
+ <li>{{Glossary("Truthy")}}</li>
+ <li>{{Glossary("Falsy")}}</li>
+</ul>
+
+<p>
+ <audio style="display: none;"></audio>
+</p>