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: Array.prototype.flat()
+slug: Web/JavaScript/Reference/Global_Objects/Array/flat
+tags:
+  - JavaScript
+  - 實驗中
+  - 方法
+  - 陣列
+translation_of: Web/JavaScript/Reference/Global_Objects/Array/flat
+---
+<div>{{JSRef}} {{SeeCompatTable}}</div>
+
+<p><code><strong>flat()</strong></code> 函數以遞迴方式將特定深度的子陣列重新串接成為一新的陣列</p>
+
+<p class="hidden">\{{EmbedInteractiveExample("pages/js/array-flatten.html")}}</p>
+
+
+
+<h2 id="語法">語法</h2>
+
+<pre class="syntaxbox"><var>var newArray = arr</var>.flat(<em>[depth]</em>);</pre>
+
+<h3 id="參數">參數</h3>
+
+<dl>
+ <dt><code>depth</code> {{optional_inline}}</dt>
+ <dd>指定巢狀陣列展開的深度。預設為1。</dd>
+</dl>
+
+<h3 id="回傳值">回傳值</h3>
+
+<p>函數將會回傳一個由原先陣列的子陣列串接而成的新陣列。</p>
+
+
+
+<h2 id="範例">範例</h2>
+
+<h3 id="展開巢狀陣列">展開巢狀陣列</h3>
+
+<pre class="brush: js">var arr1 = [1, 2, [3, 4]];
+arr1.flat();
+// [1, 2, 3, 4]
+
+var arr2 = [1, 2, [3, 4, [5, 6]]];
+arr2.flat();
+// [1, 2, 3, 4, [5, 6]]
+
+var arr3 = [1, 2, [3, 4, [5, 6]]];
+arr3.flat(2);
+// [1, 2, 3, 4, 5, 6]</pre>
+
+<h3 id="當遭遇空元素時">當遭遇空元素時</h3>
+
+<p>flat()函數會自動清除陣列中空的元素</p>
+
+<pre class="brush: js">var arr4 = [1, 2, , 4, 5];
+arr4.flat();
+// [1, 2, 4, 5]
+</pre>
+
+<h2 id="替代方案">替代方案</h2>
+
+<h3 id="reduce_與_concat"><code>reduce</code> 與 <code>concat</code></h3>
+
+<pre class="brush: js">var arr1 = [1, 2, [3, 4]];
+arr1.flat();
+
+//展開單層陣列
+arr1.reduce((acc, val) =&gt; acc.concat(val), []);// [1, 2, 3, 4]
+</pre>
+
+
+
+<pre class="brush: js">//欲展開更深層的巢狀結構請使用reduce與concat的遞迴
+function flattenDeep(arr1) {
+   return arr1.reduce((acc, val) =&gt; Array.isArray(val) ? acc.concat(flattenDeep(val)) : acc.concat(val), []);
+}
+flattenDeep(arr1);// [1, 2, 3, 1, 2, 3, 4, 2, 3, 4]
+</pre>
+
+
+
+<pre class="brush: js">//使用stack來實作非遞迴的展開
+var arr1 = [1,2,3,[1,2,3,4, [2,3,4]]];
+function flatten(input) {
+  const stack = [...input];
+  const res = [];
+  while (stack.length) {
+    // pop value from stack
+    const next = stack.pop();
+    if (Array.isArray(next)) {
+      // push back array items, won't modify the original input
+      stack.push(...next);
+    } else {
+      res.push(next);
+    }
+  }
+  //reverse to restore input order
+  return res.reverse();
+}
+flatten(arr1);// [1, 2, 3, 1, 2, 3, 4, 2, 3, 4]
+</pre>
+
+<pre><code>// 递归版本的反嵌套
+function flatten(array) {
+  var flattend = [];
+  (function flat(array) {
+    array.forEach(function(el) {
+      if (Array.isArray(el)) flat(el);
+      else flattend.push(el);
+    });
+  })(array);
+  return flattend;
+}</code></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><a href="https://tc39.github.io/proposal-flatMap/#sec-Array.prototype.flat"><code>Array.prototype.flat</code> proposal</a></td>
+   <td>Candidate (3)</td>
+   <td></td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="瀏覽器相容性">瀏覽器相容性</h2>
+
+<div>
+
+
+<p>{{Compat("javascript.builtins.Array.flat")}}</p>
+</div>
+
+<h2 id="See_also">See also</h2>
+
+<ul>
+ <li>{{jsxref("Array.prototype.flatMap()")}}</li>
+ <li>{{jsxref("Array.prototype.map()")}}</li>
+ <li>{{jsxref("Array.prototype.reduce()")}}</li>
+ <li>{{jsxref("Array.prototype.concat()")}}</li>
+</ul>
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