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+---
+title: Array.prototype.find()
+slug: Web/JavaScript/Reference/Global_Objects/Array/find
+translation_of: Web/JavaScript/Reference/Global_Objects/Array/find
+---
+<div>{{JSRef}}</div>
+
+<p><code><strong>find()</strong></code> 方法會回傳第一個滿足所提供之測試函式的元素<strong>值</strong>。否則回傳 {{jsxref("undefined")}}。</p>
+
+<div>{{EmbedInteractiveExample("pages/js/array-find.html")}}</div>
+
+
+
+<p>也可以參考 {{jsxref("Array.findIndex", "findIndex()")}} 方法，它回傳被找到的元素在陣列中的<strong>索引</strong>，而不是它的值。</p>
+
+<p>If you need to find the position of an element or whether an element exists in an array, use {{jsxref("Array.prototype.indexOf()")}} or {{jsxref("Array.prototype.includes()")}}.</p>
+
+<h2 id="語法">語法</h2>
+
+<pre class="syntaxbox"><var>arr</var>.find(<var>callback</var>[, <var>thisArg</var>])</pre>
+
+<h3 id="參數">參數</h3>
+
+<dl>
+ <dt><code>callback</code></dt>
+ <dd>會處理陣列中每個元素的函數，它使用三個參數：
+ <dl>
+  <dt><code>element</code></dt>
+  <dd>在陣列中正被處理的元素。</dd>
+  <dt><code>index</code>{{optional_inline}}</dt>
+  <dd>在陣列中正被處理的元素的索引。</dd>
+  <dt><code>array</code>{{optional_inline}}</dt>
+  <dd>呼叫 <code>find</code> 的陣列。</dd>
+ </dl>
+ </dd>
+ <dt><code>thisArg</code> <code>{{Optional_inline}}</code></dt>
+ <dd>執行 <code>callback</code> 函式時被當作 <code>this</code> 的物件。</dd>
+</dl>
+
+<h3 id="回傳值">回傳值</h3>
+
+<p>若元素通過測試則為其值；否則為 {{jsxref("undefined")}}。</p>
+
+<h2 id="描述">描述</h2>
+
+<p><code>find</code> 方法會對每個元素執行一次 <code>callback</code> 函式，直到找到一個讓 <code>callback</code> 函式回傳 true 的元素。當元素被找到的時候，<code>find</code> 會立刻回傳該元素，否則 <code>find</code> 會回傳 {{jsxref("undefined")}}。<code>callback</code> 會被使用於陣列索引自 <code>0</code> 至 <code>length - 1</code>，並會被用於每一個的陣列索引，而不僅是那些有賦值的索引。這代表此方法在稀疏陣列（sparse arrays）上的效能可能較其他只存取已賦值索引的方法來的差。</p>
+
+<p><code>callback</code> 函式被呼叫時會傳入三個參數：元素的值、元素索引，以及正被迭代的陣列物件。</p>
+
+<p>如果提供 <code>thisArg</code> 參數予 <code>find</code>，其將會被當作 <code>callback</code> 每次被呼叫的 <code>this</code>。若是沒提供，則會使用 {{jsxref("undefined")}}。</p>
+
+<p><code>find</code> 並不會改變呼叫該方法的陣列。</p>
+
+<p>The range of elements processed by <code>find</code> is set before the first invocation of <code>callback</code>. Elements that are appended to the array after the call to <code>find</code> begins will not be visited by <code>callback</code>. If an existing, unvisited element of the array is changed by <code>callback</code>, its value passed to the visiting <code>callback</code> will be the value at the time that <code>find</code> visits that element's index; elements that are deleted are still visited.</p>
+
+<h2 id="範例">範例</h2>
+
+<h3 id="Find_an_object_in_an_array_by_one_of_its_properties">Find an object in an array by one of its properties</h3>
+
+<pre class="brush: js">var inventory = [
+    {name: 'apples', quantity: 2},
+    {name: 'bananas', quantity: 0},
+    {name: 'cherries', quantity: 5}
+];
+
+function isCherries(fruit) {
+    return fruit.name === 'cherries';
+}
+
+console.log(inventory.find(isCherries));
+// { name: 'cherries', quantity: 5 }</pre>
+
+<h3 id="在陣列中找質數">在陣列中找質數</h3>
+
+<p>以下範例在陣列中找出一個屬於質數的元素，如果裡面不含質數則回傳 {{jsxref("undefined")}}。</p>
+
+<pre class="brush: js">function isPrime(element, index, array) {
+  var start = 2;
+  while (start &lt;= Math.sqrt(element)) {
+    if (element % start++ &lt; 1) {
+      return false;
+    }
+  }
+  return element &gt; 1;
+}
+
+console.log([4, 6, 8, 12].find(isPrime)); // undefined, not found
+console.log([4, 5, 8, 12].find(isPrime)); // 5
+</pre>
+
+<p>The following examples show that non-existent and deleted elements are visited and that the value passed to the callback is their value when visited.</p>
+
+<pre class="brush: js">// Declare array with no element at index 2, 3 and 4
+var a = [0,1,,,,5,6];
+
+// Shows all indexes, not just those that have been assigned values
+a.find(function(value, index) {
+  console.log('Visited index ' + index + ' with value ' + value);
+});
+
+// Shows all indexes, including deleted
+a.find(function(value, index) {
+
+  // Delete element 5 on first iteration
+  if (index == 0) {
+    console.log('Deleting a[5] with value ' + a[5]);
+    delete a[5];
+  }
+  // Element 5 is still visited even though deleted
+  console.log('Visited index ' + index + ' with value ' + value);
+});
+
+</pre>
+
+<h2 id="Polyfill">Polyfill</h2>
+
+<p>這個方法在 ECMAScript 2015 中首次被規範，可能尚未在所有 JavaScript 應用中被實作。你可以使用以下程式片段來 polyfill <code>Array.prototype.find</code>：</p>
+
+<pre class="brush: js">// https://tc39.github.io/ecma262/#sec-array.prototype.find
+if (!Array.prototype.find) {
+  Object.defineProperty(Array.prototype, 'find', {
+    value: function(predicate) {
+     // 1. Let O be ? ToObject(this value).
+      if (this == null) {
+        throw new TypeError('"this" is null or not defined');
+      }
+
+      var o = Object(this);
+
+      // 2. Let len be ? ToLength(? Get(O, "length")).
+      var len = o.length &gt;&gt;&gt; 0;
+
+      // 3. If IsCallable(predicate) is false, throw a TypeError exception.
+      if (typeof predicate !== 'function') {
+        throw new TypeError('predicate must be a function');
+      }
+
+      // 4. If thisArg was supplied, let T be thisArg; else let T be undefined.
+      var thisArg = arguments[1];
+
+      // 5. Let k be 0.
+      var k = 0;
+
+      // 6. Repeat, while k &lt; len
+      while (k &lt; len) {
+        // a. Let Pk be ! ToString(k).
+        // b. Let kValue be ? Get(O, Pk).
+        // c. Let testResult be ToBoolean(? Call(predicate, T, « kValue, k, O »)).
+        // d. If testResult is true, return kValue.
+        var kValue = o[k];
+        if (predicate.call(thisArg, kValue, k, o)) {
+          return kValue;
+        }
+        // e. Increase k by 1.
+        k++;
+      }
+
+      // 7. Return undefined.
+      return undefined;
+    }
+  });
+}
+</pre>
+
+<p>If you need to support truly obsolete JavaScript engines that don't support <code><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty">Object.defineProperty</a></code>, it's best not to polyfill <code>Array.prototype</code> methods at all, as you can't make them non-enumerable.</p>
+
+<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">備註</th>
+  </tr>
+  <tr>
+   <td>{{SpecName('ES6', '#sec-array.prototype.find', 'Array.prototype.find')}}</td>
+   <td>{{Spec2('ES6')}}</td>
+   <td>首次定義</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#sec-array.prototype.find', 'Array.prototype.find')}}</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>
+
+<div>
+
+
+<p>{{Compat("javascript.builtins.Array.find")}}</p>
+</div>
+
+<h2 id="參見">參見</h2>
+
+<ul>
+ <li>{{jsxref("Array.prototype.findIndex()")}} – find and return an index</li>
+ <li>{{jsxref("Array.prototype.includes()")}} – test whether a value exists in the array</li>
+ <li>{{jsxref("Array.prototype.filter()")}} – find all matching elements</li>
+ <li>{{jsxref("Array.prototype.every()")}} – test all elements together</li>
+</ul>