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author | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:43:23 -0500 |
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committer | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:43:23 -0500 |
commit | 218934fa2ed1c702a6d3923d2aa2cc6b43c48684 (patch) | |
tree | a9ef8ac1e1b8fe4207b6d64d3841bfb8990b6fd0 /files/zh-tw/web/javascript/reference/classes/constructor/index.html | |
parent | 074785cea106179cb3305637055ab0a009ca74f2 (diff) | |
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diff --git a/files/zh-tw/web/javascript/reference/classes/constructor/index.html b/files/zh-tw/web/javascript/reference/classes/constructor/index.html new file mode 100644 index 0000000000..8da81e9b71 --- /dev/null +++ b/files/zh-tw/web/javascript/reference/classes/constructor/index.html @@ -0,0 +1,157 @@ +--- +title: 建構子 +slug: Web/JavaScript/Reference/Classes/constructor +translation_of: Web/JavaScript/Reference/Classes/constructor +--- +<div>{{jsSidebar("Classes")}}</div> + +<p><code>constructor</code>(建構子)是個隨著 <code>class</code> 一同建立並初始化物件的特殊方法。</p> + +<h2 id="語法">語法</h2> + +<pre class="syntaxbox notranslate">constructor([arguments]) { ... }</pre> + +<h2 id="敘述">敘述</h2> + +<p>一個 class 只能有一個稱為 constructor 的特殊物件。如果一個 class 出現兩次以上的 <code>constructor</code>,就會發生 {{jsxref("SyntaxError")}} 錯誤。</p> + +<p>如果不指定建構子,就會使用預設的建構子。</p> + +<h2 id="示例">示例</h2> + +<h3 id="使用_constructor_方法">使用 <code>constructor</code> 方法</h3> + +<p>這段程式碼是從 <a href="https://github.com/GoogleChrome/samples/blob/gh-pages/classes-es6/index.html">classes sample</a> 擷取而來。(<a href="https://googlechrome.github.io/samples/classes-es6/index.html">線上範例</a>)</p> + +<pre class="brush: js notranslate">class Square extends Polygon { + constructor(length) { + // 我們在這裡呼叫了 class 的建構子提供多邊形的長寬值 + super(length, length); + // 注意:在 derived class 中,super() 必須在使用 this 以前被呼叫。不這樣的話會發生錯誤。 + this.name = 'Square'; + } + + get area() { + return this.height * this.width; + } + + set area(value) { + this.area = value; + } +}</pre> + +<h3 id="預設的建構子">預設的建構子</h3> + +<p>如上文所說:如果不指定建構子,就會使用預設的建構子。對 base classes 而言,預設的建構子長得像這樣:</p> + +<pre class="brush: js notranslate">constructor() {} +</pre> + +<p>對 derived class 而言,預設的建構子長得像這樣:</p> + +<pre class="brush: js notranslate">constructor(...args) { + super(...args); +}</pre> + +<h2 id="規範">規範</h2> + +<table class="standard-table"> + <tbody> + <tr> + <th scope="col">規範</th> + <th scope="col">狀態</th> + <th scope="col">註解</th> + </tr> + <tr> + <td>{{SpecName('ES2015', '#sec-static-semantics-constructormethod', 'Constructor Method')}}</td> + <td>{{Spec2('ES2015')}}</td> + <td>Initial definition.</td> + </tr> + <tr> + <td>{{SpecName('ESDraft', '#sec-static-semantics-constructormethod', 'Constructor Method')}}</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>功能</th> + <th>Chrome</th> + <th>Firefox (Gecko)</th> + <th>Internet Explorer</th> + <th>Opera</th> + <th>Safari</th> + </tr> + <tr> + <td>基本支援</td> + <td>{{CompatChrome(42.0)}}</td> + <td>{{CompatGeckoDesktop(45)}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatUnknown}}</td> + </tr> + <tr> + <td>預設的建構子</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatGeckoDesktop(45)}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatUnknown}}</td> + </tr> + </tbody> +</table> +</div> + +<div id="compat-mobile"> +<table class="compat-table"> + <tbody> + <tr> + <th>功能</th> + <th>Android</th> + <th>Android Webview</th> + <th>Firefox Mobile (Gecko)</th> + <th>IE Mobile</th> + <th>Opera Mobile</th> + <th>Safari Mobile</th> + <th>Chrome for Android</th> + </tr> + <tr> + <td>基本支援</td> + <td>{{CompatNo}}</td> + <td>{{CompatChrome(42.0)}}</td> + <td>{{CompatGeckoMobile(45)}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatChrome(42.0)}}</td> + </tr> + <tr> + <td>預設的建構子</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatGeckoMobile(45)}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatUnknown}}</td> + </tr> + </tbody> +</table> +</div> + +<h2 id="參見">參見</h2> + +<ul> + <li><a href="/zh-TW/docs/Web/JavaScript/Reference/Operators/super">super()</a></li> + <li><a href="/zh-TW/docs/Web/JavaScript/Reference/Operators/class"><code>class</code> expression</a></li> + <li><a href="/zh-TW/docs/Web/JavaScript/Reference/Statements/class"><code>class</code> declaration</a></li> + <li><a href="/zh-TW/docs/Web/JavaScript/Reference/Classes">Classes</a></li> +</ul> |