From 218934fa2ed1c702a6d3923d2aa2cc6b43c48684 Mon Sep 17 00:00:00 2001
From: Peter Bengtsson <mail@peterbe.com>
Date: Tue, 8 Dec 2020 14:43:23 -0500
Subject: initial commit

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+---
+title: 'null'
+slug: Web/JavaScript/Reference/Global_Objects/null
+translation_of: Web/JavaScript/Reference/Global_Objects/null
+---
+<div>{{jsSidebar("Objects")}}</div>
+
+<p>The value <code>null</code> represents the intentional absence of any object value. It is one of JavaScript's {{Glossary("Primitive", "primitive values")}}.</p>
+
+<h2 id="語法">語法</h2>
+
+<pre class="syntaxbox"><code>null </code></pre>
+
+<h2 id="描述">描述</h2>
+
+<p>The value <code>null</code> is written with a literal, <code>null</code> (it's not an identifer for a property of the global object like {{jsxref("Global_Objects/undefined","undefined")}} can be). In APIs, <code>null</code> is often retrieved in place where an object can be expected but no object is relevant. When checking for null or undefined beware of the <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators">differences between equality (==) and identity (===) operators</a> (type-conversion is performed with the former).</p>
+
+<pre class="brush: js">// foo does not exist. It is not defined and has never been initialized:
+&gt; foo
+"ReferenceError: foo is not defined"
+
+// foo is known to exist now but it has no type or value:
+&gt; var foo = null; foo
+"null"
+</pre>
+
+<h3 id="Difference_between_null_and_undefined">Difference between <code>null</code> and <code>undefined</code></h3>
+
+<pre class="brush: js">typeof null        // object (bug in ECMAScript, should be null)
+typeof undefined   // undefined
+null === undefined // false
+null  == undefined // true
+</pre>
+
+<h2 id="規範">規範</h2>
+
+<table class="standard-table">
+ <tbody>
+  <tr>
+   <th scope="col">Specification</th>
+   <th scope="col">Status</th>
+   <th scope="col">Comment</th>
+  </tr>
+  <tr>
+   <td>{{SpecName('ES1')}}</td>
+   <td>{{Spec2('ES1')}}</td>
+   <td>Initial definition.</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ES5.1', '#sec-4.3.11', 'null value')}}</td>
+   <td>{{Spec2('ES5.1')}}</td>
+   <td> </td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ES6', '#sec-null-value', 'null value')}}</td>
+   <td>{{Spec2('ES6')}}</td>
+   <td> </td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#sec-null-value', 'null value')}}</td>
+   <td>{{Spec2('ESDraft')}}</td>
+   <td> </td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="瀏覽器相容性">瀏覽器相容性</h2>
+
+<p>{{CompatibilityTable}}</p>
+
+<div id="compat-desktop">
+<table class="compat-table">
+ <tbody>
+  <tr>
+   <th>Feature</th>
+   <th>Chrome</th>
+   <th>Firefox (Gecko)</th>
+   <th>Internet Explorer</th>
+   <th>Opera</th>
+   <th>Safari</th>
+  </tr>
+  <tr>
+   <td>Basic support</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+  </tr>
+ </tbody>
+</table>
+</div>
+
+<div id="compat-mobile">
+<table class="compat-table">
+ <tbody>
+  <tr>
+   <th>Feature</th>
+   <th>Android</th>
+   <th>Chrome for Android</th>
+   <th>Firefox Mobile (Gecko)</th>
+   <th>IE Mobile</th>
+   <th>Opera Mobile</th>
+   <th>Safari Mobile</th>
+  </tr>
+  <tr>
+   <td>Basic support</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+  </tr>
+ </tbody>
+</table>
+</div>
+
+<h2 id="參見">參見</h2>
+
+<ul>
+ <li>{{jsxref("undefined")}}</li>
+ <li>{{jsxref("NaN")}}</li>
+</ul>
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