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: 區塊
+slug: Web/JavaScript/Reference/Statements/block
+translation_of: Web/JavaScript/Reference/Statements/block
+---
+<p>{{jsSidebar("Statements")}}</p>
+
+<h2 id="總覽">總覽</h2>
+
+<p>區塊陳述用來組合零個或多個陳述。我們使用一對大括號 { } 以界定區塊。</p>
+
+<table class="standard-table">
+ <tbody>
+  <tr>
+   <td class="header" colspan="2">陳述句</td>
+  </tr>
+  <tr>
+   <td>Implemented in</td>
+   <td>JavaScript 1.0</td>
+  </tr>
+  <tr>
+   <td>ECMAScript edition</td>
+   <td>ECMA-262 1st edition</td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="語法">語法</h2>
+
+<pre class="syntaxbox">{
+  <var>陳述_1</var>
+  <var>陳述_2</var>
+  ...
+  <var>陳述_n</var>
+}
+</pre>
+
+<h3 id="參數">參數</h3>
+
+<dl>
+ <dt><code>陳述_1</code>, <code>陳述_2</code>, <code>陳述_n</code></dt>
+ <dd>區塊陳述中的陳述句群。</dd>
+</dl>
+
+<h2 id="說明">說明</h2>
+
+<p>區塊陳述通常配合流程控制陳述（如 <code>if</code>、<code>for</code>、<code>while</code>）一併使用。</p>
+
+<h4 id="var"><code>var</code></h4>
+
+<p>使用<code>var</code>區塊中定義的變數，其存取範圍是整個整個函式或是腳本，即為Execution Context的範圍中。</p>
+
+<pre class="brush: js">var x = 1;
+{
+  var x = 2;
+}
+alert(x); // outputs 2
+</pre>
+
+<p>輸出結果是 2。因為var是宣告於整個腳本範圍中。</p>
+
+<h4 id="let_和_const"><code>let </code>和 <code>const</code></h4>
+
+<p>當使用<code>let</code>或是<code>const</code>進行宣告時，其存取範圍是只有本身定義的區塊中。</p>
+
+<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="keyword token">let</span> x <span class="operator token">=</span> <span class="number token">1</span><span class="punctuation token">;</span>
+<span class="punctuation token">{</span>
+  <span class="keyword token">let</span> x <span class="operator token">=</span> <span class="number token">2</span><span class="punctuation token">;</span>
+<span class="punctuation token">}</span>
+console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span>x<span class="punctuation token">)</span><span class="punctuation token">;</span> <span class="comment token">// logs 1</span></code></pre>
+
+<h4 id="function"><code>function</code></h4>
+
+<p>當function被呼叫時，會建立此function的Execution Context，因此在function區塊使用<code>var</code>整個function區塊中都可對其進行存取。</p>
+
+<pre class="brush: js">function foo() {
+    {
+        var a = 'var';
+        {
+            let a = 'let';
+            console.log(a);  // let
+        }
+    }
+    console.log(a);  // var
+}
+foo();</pre>
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