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| author | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:40:17 -0500 |
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| committer | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:40:17 -0500 |
| commit | 33058f2b292b3a581333bdfb21b8f671898c5060 (patch) | |
| tree | 51c3e392513ec574331b2d3f85c394445ea803c6 /files/zh-cn/web/javascript/reference/global_objects/set/foreach | |
| parent | 8b66d724f7caf0157093fb09cfec8fbd0c6ad50a (diff) | |
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| -rw-r--r-- | files/zh-cn/web/javascript/reference/global_objects/set/foreach/index.html | 145 |
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diff --git a/files/zh-cn/web/javascript/reference/global_objects/set/foreach/index.html b/files/zh-cn/web/javascript/reference/global_objects/set/foreach/index.html new file mode 100644 index 0000000000..e89be3af36 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/set/foreach/index.html @@ -0,0 +1,145 @@ +--- +title: Set.prototype.forEach() +slug: Web/JavaScript/Reference/Global_Objects/Set/forEach +translation_of: Web/JavaScript/Reference/Global_Objects/Set/forEach +--- +<div>{{JSRef}}</div> + +<p><code>forEach</code> 方法会根据集合中元素的插入顺序,依次执行提供的回调函数。</p> + +<h2 id="语法">语法</h2> + +<pre class="syntaxbox"><code><em>mySet</em>.forEach(<em>callback</em>[, <em>thisArg</em>])</code></pre> + +<h3 id="参数">参数</h3> + +<dl> + <dt><code>callback</code></dt> + <dd>为集合中每个元素执行的回调函数,该函数接收三个参数:</dd> + <dd> + <dl> + <dt><strong><font face="consolas, Liberation Mono, courier, monospace"><span style="background-color: rgba(220, 220, 220, 0.5);">currentValue</span>, </font></strong><strong><font face="consolas, Liberation Mono, courier, monospace"><span style="background-color: rgba(220, 220, 220, 0.5);">currentKey</span>{{optional_inline}}</font></strong></dt> + <dd><strong>currentValue</strong> 是正在被操作的元素。并且由于集合没有索引,所以 <strong>currentKey</strong> 也表示这个正在被操作的元素。</dd> + <dt><strong><font face="consolas, Liberation Mono, courier, monospace"><span style="background-color: rgba(220, 220, 220, 0.5);">set</span>{{optional_inline}}</font></strong></dt> + <dd>调用当前 <code>forEach</code> 方法的集合对象</dd> + </dl> + </dd> + <dt><code>thisArg</code><strong><font face="consolas, Liberation Mono, courier, monospace">{{optional_inline}}</font></strong></dt> + <dd>回调函数执行过程中的 <code>this</code> 值。</dd> +</dl> + +<h3 id="返回值">返回值</h3> + +<p>{{jsxref("undefined")}}.</p> + +<h2 id="描述">描述</h2> + +<p><code>forEach</code> 方法会依次为集合中的元素执行回调函数,就算元素的值是 <code>undefined </code>。</p> + +<p><strong>回调函数</strong>有三个参数:</p> + +<ul> + <li>元素的值</li> + <li>元素的索引</li> + <li>正在遍历的集合对象</li> +</ul> + +<p>但是由于集合对象中没有索引(keys),所以前两个参数都是{{domxref("Set")}}中元素的值(<strong>values</strong>),之所以这样设计回调函数是为了和{{jsxref("Map.foreach", "Map")}} 以及{{jsxref("Array.forEach","Array")}}的 <code>forEach</code> 函数用法保持一致。</p> + +<p>如果提供了一个 <code>thisArg</code> 参数给 <code>forEach</code> 函数,则参数将会作为回调函数中的 <code>this</code>值。否则 <code>this</code> 值为 <code>undefined</code>。回调函数中 <code>this</code> 的绑定是根据<a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/this">函数被调用时通用的 <code>this</code> 绑定规则来决定的</a>。</p> + +<p><code>forEach</code> 函数为集合对象中每个元素都执行一次回调;它不会返回任何值。</p> + +<h2 id="例子">例子</h2> + +<h3 id="输出集合对象的内容">输出集合对象的内容</h3> + +<p><span class="outputBox-2liU7_0">以下代码依次打印集合对象的元素:</span></p> + +<pre class="brush:js">function logSetElements(value1, value2, set) { + console.log("s[" + value1 + "] = " + value2); +} + +new Set(["foo", "bar", undefined]).forEach(logSetElements); + +// logs: +// "s[foo] = foo" +// "s[bar] = bar" +// "s[undefined] = undefined" +</pre> + +<h2 id="规范">规范</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('ES6', '#sec-set.prototype.foreach', 'Set.prototype.forEach')}}</td> + <td>{{Spec2('ES6')}}</td> + <td>Initial definition.</td> + </tr> + </tbody> +</table> + +<h2 id="浏览器兼容性">浏览器兼容性</h2> + +<p>{{CompatibilityTable}}</p> + +<div id="compat-desktop"> +<table class="compat-table"> + <tbody> + <tr> + <th>Feature</th> + <th>Chrome</th> + <th>Firefox (Gecko)</th> + <th>Internet Explorer</th> + <th>Opera</th> + <th>Safari</th> + </tr> + <tr> + <td>Basic support</td> + <td>{{ CompatChrome(38) }}</td> + <td>{{CompatGeckoDesktop("25.0")}}</td> + <td>{{ CompatIE("11") }}</td> + <td>25</td> + <td>7.1</td> + </tr> + </tbody> +</table> +</div> + +<div id="compat-mobile"> +<table class="compat-table"> + <tbody> + <tr> + <th>Feature</th> + <th>Android</th> + <th>Chrome for Android</th> + <th>Firefox Mobile (Gecko)</th> + <th>IE Mobile</th> + <th>Opera Mobile</th> + <th>Safari Mobile</th> + </tr> + <tr> + <td>Basic support</td> + <td>{{CompatNo}}</td> + <td>38</td> + <td>{{CompatGeckoMobile("25.0")}}</td> + <td>{{CompatNo}}</td> + <td>{{CompatNo}}</td> + <td>8</td> + </tr> + </tbody> +</table> +</div> + +<h2 id="参见">参见</h2> + +<ul> + <li>{{jsxref("Array.prototype.forEach()")}}</li> + <li>{{jsxref("Map.prototype.forEach()")}}</li> +</ul> |
