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diff --git a/files/zh-tw/web/javascript/reference/global_objects/null/index.html b/files/zh-tw/web/javascript/reference/global_objects/null/index.html new file mode 100644 index 0000000000..0af88facab --- /dev/null +++ b/files/zh-tw/web/javascript/reference/global_objects/null/index.html @@ -0,0 +1,124 @@ +--- +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: +> foo +"ReferenceError: foo is not defined" + +// foo is known to exist now but it has no type or value: +> 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> |