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135 lines
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135 lines
9.8 KiB
HTML
<article id="wikiArticle">
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<div></div>
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<p><code><strong>Math.trunc()</strong></code> 方法会将数字的小数部分去掉，只保留整数部分。</p>
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<h2 id="Syntax" name="Syntax">语法</h2>
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<pre><code class="language-javascript">Math.trunc(<em>value</em>)</code></pre>
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<h3 id="Parameters" name="Parameters">参数</h3>
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<dl>
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<dt><code>value</code></dt>
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<dd>任意数字</dd>
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</dl>
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<h3 id="返回值">返回值</h3>
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<p>给定数字的整数部分</p>
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<h2 id="Description" name="Description">描述</h2>
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<p>不像 <code>Math</code> 的其他三个方法： <a href="Reference/Global_Objects/Math/floor" title="Math.floor() 返回小于或等于一个给定数字的最大整数。"><code>Math.floor()</code></a>、<a href="Reference/Global_Objects/Math/ceil" title="Math.ceil() 函数返回大于或等于一个给定数字的最小整数。"><code>Math.ceil()</code></a>、<a href="Reference/Global_Objects/Math/round" title="Math.round() 函数返回一个数字四舍五入后最接近的整数。"><code>Math.round()</code></a> ，<code>Math.trunc()</code> 的执行逻辑很简单，仅仅是<strong>删除</strong>掉数字的小数部分和小数点，不管参数是正数还是负数。</p>
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<p>传入该方法的参数会被隐式转换成数字类型。</p>
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<p>因为 <code>trunc()</code> 是 <code>Math</code> 对象的静态方法，你必须用 <code>Math.trunc()</code> 来使用，而不是调用你创建的 <code>Math</code> 对象的一个实例方法（<code>Math</code> 没有构造函数）</p>
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<h2 id="Examples" name="Examples">示例</h2>
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<pre><code class="language-js">Math.trunc(13.37) // 13
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Math.trunc(42.84) // 42
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Math.trunc(0.123) // 0
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Math.trunc(-0.123) // -0
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Math.trunc("-1.123") // -1
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Math.trunc(NaN) // NaN
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Math.trunc("foo") // NaN
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Math.trunc() // NaN</code></pre>
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<h2 id="Polyfill">Polyfill</h2>
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<pre><code>if (!Math.trunc) {
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Math.trunc = function(v) {
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v = +v;
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if (!isFinite(v)) return v;
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return (v - v % 1) || (v < 0 ? -0 : v === 0 ? v : 0);
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// 返回:
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// 0 -> 0
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// -0 -> -0
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// 0.2 -> 0
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// -0.2 -> -0
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// 0.7 -> 0
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// -0.7 -> -0
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// Infinity -> Infinity
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// -Infinity -> -Infinity
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// NaN -> NaN
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// null -> 0
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};
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}</code>
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</code></pre>
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<p>或:</p>
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<pre><code>if (!Math.trunc) {
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Math.trunc = function(v) {
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v = +v;
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return (v - v % 1) || (!isFinite(v) || v === 0 ? v : v < 0 ? -0 : 0);
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};
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}</code></code></pre>
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<h2 id="规范">规范</h2>
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<table class="standard-table">
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<tbody>
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<tr>
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<th scope="col">规范名称</th>
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<th scope="col">规范状态</th>
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<th scope="col">备注</th>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-math.trunc" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Math.trunc</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td> </td>
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</tr>
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<tr>
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<td><a class="external" href="https://tc39.github.io/ecma262/#sec-math.trunc" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Math.trunc</small></a></td>
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<td><span class="spec-Draft">Draft</span></td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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<h2 id="浏览器兼容性">浏览器兼容性</h2>
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<p></p><div class="bc-data"><a class="bc-github-link external" href="https://github.com/mdn/browser-compat-data" rel="noopener">Update compatibility data on GitHub</a><table class="bc-table bc-table-js"><thead><tr class="bc-platforms"><td></td><th class="bc-platform-desktop" colspan="6"><span>Desktop</span></th><th class="bc-platform-mobile" colspan="7"><span>Mobile</span></th><th class="bc-platform-server" colspan="1"><span>Server</span></th></tr><tr class="bc-browsers"><td></td><th class="bc-browser-chrome"><span class="bc-head-txt-label bc-head-icon-chrome">Chrome</span></th><th class="bc-browser-edge"><span class="bc-head-txt-label bc-head-icon-edge">Edge</span></th><th class="bc-browser-firefox"><span class="bc-head-txt-label bc-head-icon-firefox">Firefox</span></th><th class="bc-browser-ie"><span class="bc-head-txt-label bc-head-icon-ie">Internet Explorer</span></th><th class="bc-browser-opera"><span class="bc-head-txt-label bc-head-icon-opera">Opera</span></th><th class="bc-browser-safari"><span class="bc-head-txt-label bc-head-icon-safari">Safari</span></th><th class="bc-browser-webview_android"><span class="bc-head-txt-label bc-head-icon-webview_android">Android webview</span></th><th class="bc-browser-chrome_android"><span class="bc-head-txt-label bc-head-icon-chrome_android">Chrome for Android</span></th><th class="bc-browser-edge_mobile"><span class="bc-head-txt-label bc-head-icon-edge_mobile">Edge Mobile</span></th><th class="bc-browser-firefox_android"><span class="bc-head-txt-label bc-head-icon-firefox_android">Firefox for Android</span></th><th class="bc-browser-opera_android"><span class="bc-head-txt-label bc-head-icon-opera_android">Opera for Android</span></th><th class="bc-browser-safari_ios"><span class="bc-head-txt-label bc-head-icon-safari_ios">Safari on iOS</span></th><th class="bc-browser-samsunginternet_android"><span class="bc-head-txt-label bc-head-icon-samsunginternet_android">Samsung Internet</span></th><th class="bc-browser-nodejs"><span class="bc-head-txt-label bc-head-icon-nodejs">Node.js</span></th></tr></thead><tbody><tr><th scope="row"><code>trunc</code></th><td class="bc-supports-yes bc-browser-chrome"><span class="bc-browser-name">Chrome</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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38</td><td class="bc-supports-yes bc-browser-edge"><span class="bc-browser-name">Edge</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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12</td><td class="bc-supports-yes bc-browser-firefox"><span class="bc-browser-name">Firefox</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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25</td><td class="bc-supports-no bc-browser-ie"><span class="bc-browser-name">IE</span><abbr class="bc-level-no only-icon" title="No support">
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<span>No support</span>
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</abbr>
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No</td><td class="bc-supports-yes bc-browser-opera"><span class="bc-browser-name">Opera</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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25</td><td class="bc-supports-yes bc-browser-safari"><span class="bc-browser-name">Safari</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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8</td><td class="bc-supports-yes bc-browser-webview_android"><span class="bc-browser-name">WebView Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-chrome_android"><span class="bc-browser-name">Chrome Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-edge_mobile"><span class="bc-browser-name">Edge Mobile</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-firefox_android"><span class="bc-browser-name">Firefox Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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25</td><td class="bc-supports-yes bc-browser-opera_android"><span class="bc-browser-name">Opera Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-safari_ios"><span class="bc-browser-name">Safari iOS</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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8</td><td class="bc-supports-yes bc-browser-samsunginternet_android"><span class="bc-browser-name">Samsung Internet Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-nodejs"><span class="bc-browser-name">nodejs</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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0.12</td></tr></tbody></table><section class="bc-legend" id="sect1"><h3 class="offscreen" id="Legend">Legend</h3><dl><dt><span class="bc-supports-yes bc-supports">
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<abbr class="bc-level bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr></span></dt><dd>Full support</dd><dt><span class="bc-supports-no bc-supports">
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<abbr class="bc-level bc-level-no only-icon" title="No support">
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<span>No support</span>
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</abbr></span></dt><dd>No support</dd></dl></section></div><p></p>
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<p><strong style="color: #4d4e53; font-size: 2.14286rem; font-weight: 700; letter-spacing: -1px;">相关链接</strong></p>
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<ul>
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<li><a href="Reference/Global_Objects/Math/abs" title="Math.abs(x) 函数返回指定数字 “x“ 的绝对值。如下："><code>Math.abs()</code></a></li>
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<li><a href="Reference/Global_Objects/Math/ceil" title="Math.ceil() 函数返回大于或等于一个给定数字的最小整数。"><code>Math.ceil()</code></a></li>
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<li><a href="Reference/Global_Objects/Math/floor" title="Math.floor() 返回小于或等于一个给定数字的最大整数。"><code>Math.floor()</code></a></li>
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<li><a href="Reference/Global_Objects/Math/round" title="Math.round() 函数返回一个数字四舍五入后最接近的整数。"><code>Math.round()</code></a></li>
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<li><a href="Reference/Global_Objects/Math/sign" title="Math.sign() 函数返回一个数字的符号, 指示数字是正数，负数还是零。"><code>Math.sign()</code></a></li>
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</ul>
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</article> |