From da78a9e329e272dedb2400b79a3bdeebff387d47 Mon Sep 17 00:00:00 2001
From: Peter Bengtsson <mail@peterbe.com>
Date: Tue, 8 Dec 2020 14:42:17 -0500
Subject: initial commit

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+---
+title: Array.prototype.flat()
+slug: Web/JavaScript/Reference/Global_Objects/Array/flat
+tags:
+  - Array
+  - JavaScript
+  - Method
+  - Prototype
+  - Reference
+translation_of: Web/JavaScript/Reference/Global_Objects/Array/flat
+---
+<div>{{JSRef}}</div>
+
+<p><code><strong>flat()</strong></code> 메서드는 모든 하위 배열 요소를 지정한 깊이까지 재귀적으로 이어붙인 새로운 배열을 생성합니다.</p>
+
+<h2 id="구문">구문</h2>
+
+<pre class="syntaxbox">const <em>newArr</em> = <em>arr</em>.flat([<em>depth</em>])</pre>
+
+<h3 id="매개변수">매개변수</h3>
+
+<dl>
+ <dt><code>depth</code> {{optional_inline}}</dt>
+ <dd>중첩 배열 구조를 평탄화할 때 사용할 깊이 값. 기본값은 1입니다.</dd>
+</dl>
+
+<h3 id="반환_값">반환 값</h3>
+
+<p>하위 배열을 이어붙인 새로운 배열.</p>
+
+<h2 id="예제">예제</h2>
+
+<h3 id="중첩_배열_평탄화">중첩 배열 평탄화</h3>
+
+<pre class="brush: js">const arr1 = [1, 2, [3, 4]];
+arr1.flat();
+// [1, 2, 3, 4]
+
+const arr2 = [1, 2, [3, 4, [5, 6]]];
+arr2.flat();
+// [1, 2, 3, 4, [5, 6]]
+
+const arr3 = [1, 2, [3, 4, [5, 6]]];
+arr3.flat(2);
+// [1, 2, 3, 4, 5, 6]
+
+const arr4 = [1, 2, [3, 4, [5, 6, [7, 8, [9, 10]]]]];
+arr4.flat(Infinity);
+// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]</pre>
+
+<h3 id="배열_구멍_제거">배열 구멍 제거</h3>
+
+<p><code>flat</code> 메서드는 배열의 구멍도 제거합니다.</p>
+
+<pre class="brush: js">const arr5 = [1, 2, , 4, 5];
+arr5.flat();
+// [1, 2, 4, 5]</pre>
+
+<h2 id="대안">대안</h2>
+
+<h3 id="reduce와_concat"><code>reduce</code>와 <code>concat</code></h3>
+
+<pre class="brush: js">const arr = [1, 2, [3, 4]];
+
+// To flat single level array
+arr.flat();
+// is equivalent to
+arr.reduce((acc, val) =&gt; acc.concat(val), []);
+// [1, 2, 3, 4]
+
+// or with decomposition syntax
+const flattened = arr =&gt; [].concat(...arr);</pre>
+
+<h3 id="reduce_concat_isArray_재귀"><code>reduce</code> + <code>concat</code> + <code>isArray</code> + 재귀</h3>
+
+<pre class="brush: js">const arr = [1, 2, [3, 4, [5, 6]]];
+
+// to enable deep level flatten use recursion with reduce and concat
+function flatDeep(arr, d = 1) {
+   return d &gt; 0 ? arr.reduce((acc, val) =&gt; acc.concat(Array.isArray(val) ? flatDeep(val, d - 1) : val), [])
+                : arr.slice();
+};
+
+flatDeep(arr, Infinity);
+// [1, 2, 3, 4, 5, 6]</pre>
+
+<h3 id="스택">스택</h3>
+
+<pre class="brush: js">// non recursive flatten deep using a stack
+// note that depth control is hard/inefficient as we will need to tag EACH value with its own depth
+// also possible w/o reversing on shift/unshift, but array OPs on the end tends to be faster
+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();
+}
+
+const arr = [1, 2, [3, 4, [5, 6]]];
+flatten(arr);
+// [1, 2, 3, 4, 5, 6]</pre>
+
+<h3 id="Generator_함수"><code>Generator</code> 함수</h3>
+
+<pre class="brush: js">function* flatten(array, depth) {
+    if(depth === undefined) {
+      depth = 1;
+    }
+    for(const item of array) {
+        if(Array.isArray(item) &amp;&amp; depth &gt; 0) {
+          yield* flatten(item, depth - 1);
+        } else {
+          yield item;
+        }
+    }
+}
+
+const arr = [1, 2, [3, 4, [5, 6]]];
+const flattened = [...flatten(arr, Infinity)];
+// [1, 2, 3, 4, 5, 6]</pre>
+
+<h2 id="명세">명세</h2>
+
+<table class="standard-table">
+ <tbody>
+  <tr>
+   <th scope="col">Specification</th>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#sec-array.prototype.flat', 'Array.prototype.flat')}}</td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="브라우저_호환성">브라우저 호환성</h2>
+
+<div>
+
+
+<p>{{Compat("javascript.builtins.Array.flat")}}</p>
+</div>
+
+<h2 id="같이_보기">같이 보기</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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