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204 lines
8.1 KiB
HTML
<article id="wikiArticle">
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<div><br/>
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</div>
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<p><code><strong>Math.floor()</strong></code> 返回小于或等于一个给定数字的最大整数。</p>
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<div class="note">
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<p>Note: <code><strong>Math.floor() === </strong></code>向下取整</p>
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</div>
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<h2 id="Syntax" name="Syntax">语法</h2>
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<pre><code class="language-javascript"><code>Math.floor(<em>x</em>) </code></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>x</code></dt>
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<dd>一个数字。</dd>
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<dt>
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<h3 id="返回值">返回值 </h3>
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<p>一个表示小于或等于指定数字的最大整数的数字。</p>
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</dt>
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</dl>
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<h2 id="Description" name="Description">描述</h2>
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<p>由于 <code>floor</code> 是 <code>Math</code> 的一个静态方法，你总是应该像这样使用它 <code>Math.floor()</code>，而不是作为你创建的一个Math对象的一种方法（Math不是一个构造函数）。</p>
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<h2 id="Examples" name="Examples">示例</h2>
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<h3 id="Example:_Using_Math.floor" name="Example:_Using_Math.floor">例子：使用 <code>Math.floor</code></h3>
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<pre><code class="language-js">Math.floor( 45.95);
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// 45
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Math.floor( 45.05);
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// 45
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Math.floor( 4 );
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// 4
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Math.floor(-45.05);
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// -46
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Math.floor(-45.95);
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// -46
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</code></pre>
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<h3 id="Example:_Decimal_adjustment" name="Example:_Decimal_adjustment">例子：十进制调整</h3>
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<pre><code class="language-js">// Closure
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(function(){
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/**
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* Decimal adjustment of a number.
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*
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* @param {String} type The type of adjustment.
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* @param {Number} value The number.
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* @param {Integer} exp The exponent (the 10 logarithm of the adjustment base).
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* @returns {Number} The adjusted value.
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*/
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function decimalAdjust(type, value, exp) {
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// If the exp is undefined or zero...
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if (typeof exp === 'undefined' || +exp === 0) {
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return Math[type](value);
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}
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value = +value;
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exp = +exp;
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// If the value is not a number or the exp is not an integer...
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if (isNaN(value) || !(typeof exp === 'number' && exp % 1 === 0)) {
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return NaN;
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}
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// Shift
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value = value.toString().split('e');
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value = Math[type](+(value[0] + 'e' + (value[1] ? (+value[1] - exp) : -exp)));
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// Shift back
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value = value.toString().split('e');
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return +(value[0] + 'e' + (value[1] ? (+value[1] + exp) : exp));
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}
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// Decimal round
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if (!Math.round10) {
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Math.round10 = function(value, exp) {
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return decimalAdjust('round', value, exp);
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};
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}
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// Decimal floor
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if (!Math.floor10) {
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Math.floor10 = function(value, exp) {
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return decimalAdjust('floor', value, exp);
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};
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}
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// Decimal ceil
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if (!Math.ceil10) {
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Math.ceil10 = function(value, exp) {
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return decimalAdjust('ceil', value, exp);
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};
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}
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})();
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// Round
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Math.round10(55.55, -1); // 55.6
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Math.round10(55.549, -1); // 55.5
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Math.round10(55, 1); // 60
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Math.round10(54.9, 1); // 50
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Math.round10(-55.55, -1); // -55.5
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Math.round10(-55.551, -1); // -55.6
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Math.round10(-55, 1); // -50
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Math.round10(-55.1, 1); // -60
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// Floor
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Math.floor10(55.59, -1); // 55.5
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Math.floor10(59, 1); // 50
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Math.floor10(-55.51, -1); // -55.6
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Math.floor10(-51, 1); // -60
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// Ceil
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Math.ceil10(55.51, -1); // 55.6
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Math.ceil10(51, 1); // 60
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Math.ceil10(-55.59, -1); // -55.5
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Math.ceil10(-59, 1); // -50
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</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">规范版本</th>
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<th scope="col">规范状态</th>
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<th scope="col">注解</th>
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</tr>
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<tr>
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<td>ECMAScript 1st Edition. Implemented in JavaScript 1.0</td>
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<td>Standard</td>
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<td>Initial definition.</td>
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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-262/5.1/#sec-15.8.2.9" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">Math.floor</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://www.ecma-international.org/ecma-262/6.0/#sec-math.floor" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Math.floor</small></a><span style="display: none;"> </span></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.floor" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Math.floor</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="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
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This compatibility table still uses the old format,
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because we haven't yet converted the data it contains.
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<strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
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<div class="htab">
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<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
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<ul>
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<li class="selected"><a>Desktop</a></li>
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<li><a>Mobile</a></li>
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</ul>
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</div><p></p>
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<div id="compat-desktop">
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<table class="compat-table">
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<tbody>
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<tr>
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<th>Feature</th>
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<th>Chrome</th>
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<th>Firefox (Gecko)</th>
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<th>Internet Explorer</th>
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<th>Opera</th>
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<th>Safari</th>
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</tr>
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<tr>
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<td>Basic support</td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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</tr>
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</tbody>
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</table>
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</div>
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<div id="compat-mobile">
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<table class="compat-table">
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<tbody>
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<tr>
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<th>Feature</th>
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<th>Android</th>
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<th>Chrome for Android</th>
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<th>Firefox Mobile (Gecko)</th>
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<th>IE Mobile</th>
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<th>Opera Mobile</th>
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<th>Safari Mobile</th>
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</tr>
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<tr>
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<td>Basic support</td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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</tr>
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</tbody>
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</table>
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</div>
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<h2 id="See_also" name="See_also">相关链接</h2>
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<ul>
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<li>The <a href="Reference/Global_Objects/Math" title="Math 是一个内置对象， 它具有数学常数和函数的属性和方法。不是一个函数对象。"><code>Math</code></a> object it belongs to.</li>
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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/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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<li><a href="Reference/Global_Objects/Math/trunc" title="Math.trunc() 方法会将数字的小数部分去掉，只保留整数部分。"><code>Math.trunc()</code></a></li>
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</ul>
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</article> |