---
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>

<h2 id="语法">语法</h2>

<pre class="syntaxbox">!<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">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">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">!!bCondition</pre>

<p>is always equal to:</p>

<pre class="brush: js">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>