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+---
+title: label
+slug: Web/JavaScript/Reference/Statements/label
+tags:
+  - JavaScript
+  - Statement
+  - 陳述式
+translation_of: Web/JavaScript/Reference/Statements/label
+---
+<div>{{jsSidebar("Statements")}}</div>
+
+<p><strong>標記陳述式</strong>可以和 {{jsxref("Statements/break", "break")}} 或 {{jsxref("Statements/continue", "continue")}} 語句一起使用。標記就是在一條陳述式前面加個可以引用的識別符號。</p>
+
+<div>{{EmbedInteractiveExample("pages/js/statement-label.html")}}</div>
+
+
+
+<div class="note">
+<p>標記的迴圈或程式碼區塊非常罕見。通常可以使用函式呼叫而不是使用迴圈跳轉。</p>
+</div>
+
+<h2 id="語法">語法</h2>
+
+<pre class="syntaxbox"><em>label</em> :
+   <em>statement</em>
+</pre>
+
+<dl>
+ <dt><code>label</code></dt>
+ <dd>任何不是保留字的 JavaScript 識別符號。</dd>
+ <dt><code>statement</code></dt>
+ <dd>一個 JavaScript 陳述式。<code>break</code> 可用於任何標記陳述式，而 <code>continue</code> 可用於循環標記陳述式。</dd>
+</dl>
+
+<h2 id="描述">描述</h2>
+
+<p>可使用一個標籤來唯一標記一個循環，然後使用 <code>break</code> 或 <code>continue</code> 陳述式來指示程式是否中斷循環或繼續執行。</p>
+
+<p>需要注意的是 JavaScript <strong>沒有</strong> <code>goto</code> 陳述式，標記只能和 <code>break</code> 或 <code>continue</code> 一起使用。</p>
+
+<p>在<a href="https://developer.mozilla.org/zh-TW/docs/Web/JavaScript/Reference/Strict_mode">嚴格模式</a>中，你不能使用 “<code>let</code>” 作為標籤名稱。它會拋出一個<a href="https://developer.mozilla.org/zh-TW/docs/Web/JavaScript/Reference/Global_Objects/SyntaxError" title="SyntaxError 物件代表嘗試解析語法上不合法的程式碼的錯誤。"><code>SyntaxError</code></a>（let 是一個保留的識別符號）。</p>
+
+<h2 id="範例">範例</h2>
+
+<h3 id="在_for_迴圈中使用帶標記的_continue">在 <code>for</code> 迴圈中使用帶標記的 <code>continue</code> </h3>
+
+<pre class="brush: js">var i, j;
+
+loop1:
+for (i = 0; i &lt; 3; i++) {      //The first for statement is labeled "loop1"
+   loop2:
+   for (j = 0; j &lt; 3; j++) {   //The second for statement is labeled "loop2"
+      if (i === 1 &amp;&amp; j === 1) {
+         continue loop1;
+      }
+      console.log('i = ' + i + ', j = ' + j);
+   }
+}
+
+// Output is:
+//   "i = 0, j = 0"
+//   "i = 0, j = 1"
+//   "i = 0, j = 2"
+//   "i = 1, j = 0"
+//   "i = 2, j = 0"
+//   "i = 2, j = 1"
+//   "i = 2, j = 2"
+// Notice how it skips both "i = 1, j = 1" and "i = 1, j = 2"
+</pre>
+
+<h3 id="使用帶標記的_continue_陳述式">使用帶標記的 <code>continue</code> 陳述式</h3>
+
+<p>給定一組資料和一組測試，下面的例子可以統計通過測試的資料。</p>
+
+<pre class="brush: js">var itemsPassed = 0;
+var i, j;
+
+top:
+for (i = 0; i &lt; items.length; i++) {
+  for (j = 0; j &lt; tests.length; j++) {
+    if (!tests[j].pass(items[i])) {
+      continue top;
+    }
+  }
+
+  itemsPassed++;
+}</pre>
+
+<h3 id="在_for_迴圈中使用帶標記的_break">在 <code>for</code> 迴圈中使用帶標記的 <font face="consolas, Liberation Mono, courier, monospace"><span style="background-color: rgba(255, 255, 255, 0.4);">break</span></font> </h3>
+
+<pre class="brush: js">var i, j;
+
+loop1:
+for (i = 0; i &lt; 3; i++) {      //The first for statement is labeled "loop1"
+   loop2:
+   for (j = 0; j &lt; 3; j++) {   //The second for statement is labeled "loop2"
+      if (i === 1 &amp;&amp; j === 1) {
+         break loop1;
+      }
+      console.log('i = ' + i + ', j = ' + j);
+   }
+}
+
+// Output is:
+//   "i = 0, j = 0"
+//   "i = 0, j = 1"
+//   "i = 0, j = 2"
+//   "i = 1, j = 0"
+// Notice the difference with the previous continue example</pre>
+
+<h3 id="使用帶標記_break_陳述式">使用帶標記 <code>break</code> 陳述式</h3>
+
+<p>給定一組資料和一組測試，下面的例子判斷是否所有的資料均通過了測試。</p>
+
+<pre class="brush: js">var allPass = true;
+var i, j;
+
+top:
+for (i = 0; items.length; i++)
+  for (j = 0; j &lt; tests.length; i++)
+    if (!tests[j].pass(items[i])) {
+      allPass = false;
+      break top;
+    }</pre>
+
+<h3 id="在標記的區塊中使用_break">在標記的區塊中使用 <code>break</code></h3>
+
+<p>你可以在程式碼區塊中使用標記，但只有 <code>break</code> 陳述式可以使用非迴圈的標記。</p>
+
+<pre class="brush: js">foo: {
+  console.log('face');
+  break foo;
+  console.log('this will not be executed');
+}
+console.log('swap');
+
+// this will log:
+
+// "face"
+// "swap </pre>
+
+<h3 id="標記的函式宣告式">標記的函式宣告式</h3>
+
+<p>從 ECMAScript 2015 開始，標準的函式宣告式現在對規範的 <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-labelled-function-declarations" rel="noopener">Web 相容性附件</a>中的非嚴格程式碼進行了標準化。</p>
+
+<pre class="brush: js">L: function F() {}</pre>
+
+<p>在<a href="https://developer.mozilla.org/zh-TW/docs/Web/JavaScript/Reference/Strict_mode">嚴格模式</a>中，這會拋出 {{jsxref("SyntaxError")}} 例外：</p>
+
+<pre class="brush: js">'use strict';
+L: function F() {}
+// SyntaxError: functions cannot be labelled</pre>
+
+<p><a href="https://developer.mozilla.org/zh-TW/docs/Web/JavaScript/Reference/Statements/function*">產生器函式</a>既不能在嚴格模式中標記，也不能在非嚴格模式中標記：</p>
+
+<pre class="brush: js">L: function* F() {}
+// SyntaxError: generator functions cannot be labelled
+</pre>
+
+<h2 id="規格">規格</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('ES3')}}</td>
+   <td>{{Spec2('ES3')}}</td>
+   <td>Initial definition. Implemented in JavaScript 1.2</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ES5.1', '#sec-12.12', 'Labelled statement')}}</td>
+   <td>{{Spec2('ES5.1')}}</td>
+   <td> </td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ES6', '#sec-labelled-statements', 'Labelled statement')}}</td>
+   <td>{{Spec2('ES6')}}</td>
+   <td> </td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#sec-labelled-statements', 'Labelled statement')}}</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>{{Compat("javascript.statements.label")}}</p>
+
+<h2 id="相關連結">相關連結</h2>
+
+<ul>
+ <li>{{jsxref("Statements/break", "break")}}</li>
+ <li>{{jsxref("Statements/continue", "continue")}}</li>
+</ul>