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265 lines
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HTML
265 lines
19 KiB
HTML
<article id="wikiArticle">
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<p></p><p></p>
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<p><code><strong>Math.round()</strong></code> 函数返回一个数字四舍五入后最接近的整数。</p>
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<h2 id="Syntax" name="Syntax">语法</h2>
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<pre><code class="language-javascript"><code>Math.round(<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>一个数值。</dd>
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<dt>
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<h3 id="返回值">返回值</h3>
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<p>给定数字的值四舍五入到最接近的整数。</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>如果参数的小数部分大于 0.5,则舍入到相邻的绝对值更大的整数。 如果参数的小数部分小于 0.5,则舍入到相邻的绝对值更小的整数。如果参数的小数部分恰好等于0.5,则舍入到相邻的在正无穷(+∞)方向上的整数。<strong>注意,与很多其他语言中的<code>round()函数</code>不同,<code>Math.round()并不总是舍入到远离0的方向(尤其是在负数的小数部分恰好等于0.5的情况下)。</code></strong></p>
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<p>因为 <code>round()</code> 是 <code>Math</code> 的静态方法,你应该直接使用 <code>Math.round()</code>,而不是作为你创建的 <code>Math</code> 对象的一个实例方法来使用(<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">x = Math.round(20.49); //20
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x = Math.round(20.5); //21
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x = Math.round(-20.5); //-20
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x = Math.round(-20.51); //-21
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</code></pre>
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<h3 id="Example:_Decimal_rounding" name="Example:_Decimal_rounding" style="line-height: 24px;">小数舍入</h3>
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<pre><code class="language-javascript">// 闭包
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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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Math.round10(1.005, -2); // 1.01 -- compare this with Math.round(1.005*100)/100 above
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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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<p>或:</p>
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<pre><code class="language-javascript">function round(number, precision) {
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return Math.round(+number + 'e' + precision) / Math.pow(10, precision);
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//same as:
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//return Number(Math.round(+number + 'e' + precision) + 'e-' + precision);
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}
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round(1.005, 2); //1.01
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</code></pre>
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<h2 id="规范" style="margin-bottom: 20px; line-height: 30px;">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-15.8.2.15" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">Math.round</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.round" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Math.round</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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</tbody>
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</table>
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<h2 id="浏览器兼容性" style="margin-bottom: 20px; line-height: 30px;">浏览器兼容性</h2>
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<div><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></div>
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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 style="line-height: 16px;">Feature</th>
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<th style="line-height: 16px;">Chrome</th>
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<th style="line-height: 16px;">Firefox (Gecko)</th>
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<th style="line-height: 16px;">Internet Explorer</th>
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<th style="line-height: 16px;">Opera</th>
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<th style="line-height: 16px;">Safari (WebKit)</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 style="line-height: 16px;">Feature</th>
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<th style="line-height: 16px;">Android</th>
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<th style="line-height: 16px;">Firefox Mobile (Gecko)</th>
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<th style="line-height: 16px;">IE Phone</th>
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<th style="line-height: 16px;">Opera Mobile</th>
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<th style="line-height: 16px;">Safari Mobile</th>
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</tr>
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<tr>
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<td>Basic support</td>
|
||
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
|
||
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
|
||
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
|
||
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
|
||
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
</div>
|
||
<h2 id="See_also" name="See_also" style="margin-bottom: 20px; line-height: 30px;">相关链接</h2>
|
||
<p></p>
|
||
<ul>
|
||
<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>
|
||
<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>
|
||
<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>
|
||
</ul>
|
||
</article> |