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uTools-Manuals/docs/javascript/Reference/Global_Objects/Math/random.html
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<article id="wikiArticle">
<div></div>
<div> </div>
<p><code><strong>Math.random()</strong></code> 函数返回一个浮点,  伪随机数在范围<strong>[0，1)</strong>，也就是说，从0（包括0）往上，但是不包括1（排除1），然后您可以缩放到所需的范围。实现将初始种子选择到随机数生成算法;它不能被用户选择或重置。</p>
<p><iframe class="interactive interactive-js" frameborder="0" height="250" src="https://interactive-examples.mdn.mozilla.net/pages/js/math-random.html" width="100%"></iframe></p>
<div class="note">
<p>[0，1) === [即从0（包含0）到...1但不包括1（排除1）。</p>
<p>[0，1) === 左闭右开区间</p>
</div>
<div class="note">
<p><code>Math.random()</code> <em>不能提供像密码一样安全的随机数字</em></p>
<p>不能使用它们来处理有关安全的事情。使用Web Crypto API 来代替, 和更精确的<a href="/zh-CN/docs/Web/API/RandomSource/getRandomValues" title="RandomSource.getRandomValues() 方法让你可以获取符合密码学要求的安全的随机值。传入参数的数组被随机值填充（在加密意义上的随机）。"><code>window.crypto.getRandomValues()</code></a> 方法.</p>
</div>
<h2 id="Syntax" name="Syntax">语法</h2>
<pre><code class="language-javascript"><code>Math.random()</code></code></pre>
<h3 id="Parameters" name="Parameters">返回参数</h3>
<p>一个浮点型伪随机数字，在<code>0</code>（包括0）和<code>1</code>（不包括）之间。</p>
<h2 id="Examples" name="Examples">示例</h2>
<p>Note that as numbers in JavaScript are IEEE 754 floating point numbers with round-to-nearest-even behavior, the ranges claimed for the functions below (excluding the one for <code>Math.random()</code> itself) aren't exact. If extremely large bounds are chosen (2<sup>53</sup> or higher), it's possible in <em>extremely</em> rare cases to calculate the usually-excluded upper bound. （注：round-to-nearest-even采用最近舍入的去偶数舍入的方式，对.5的舍入上，采用取偶数的方式）</p>
<p>请注意, 由于 JavaScript 中的数字是 IEEE 754 浮点数字，具有最近舍入（ round-to-nearest-even）的行为, 因此以下函数的范围 (不包括Math.random () 本身) 并不准确。如果选择了非常大的边界 (2<sup>53</sup> 或更高), 在极罕见的情况下会计算通常-排除（usually-excluded）的上界。</p>
<p>IEEE 754标准的默认模式是最近舍入（舍入为最接近的偶数），它与四舍五入不同的是，对.5的舍入上采用取偶数的方式，即round-to-nearest-even，如：</p>
<p>Round to nearest even：Round(0.5) = 0; Round(1.5) = 2; Round(2.5) = 2;Round(3.5) = 4;</p>
<p>即："四舍六入五取偶"<br/>
“五取偶”的规则：当小数部分恰为0.5时，若个位是奇数则入，若个位是偶数则舍，总之让个位变成偶数。</p>
<h3 id="得到一个大于等于0，小于1之间的随机数">得到一个大于等于0，小于1之间的随机数</h3>
<pre><code class="language-javascript">function getRandom() {
return Math.random();
}</code></pre>
<h3 id="得到一个两数之间的随机数">得到一个两数之间的随机数</h3>
<p>这个例子返回了一个在指定值之间的随机数。这个值不小于 <code>min</code>（有可能等于），并且小于（不等于）<code>max</code>。</p>
<pre><code class="language-javascript">function getRandomArbitrary(min, max) {
return Math.random() * (max - min) + min;
}</code></pre>
<h3 id="得到一个两数之间的随机整数">得到一个两数之间的随机整数</h3>
<p>这个例子返回了一个在指定值之间的随机整数。这个值不小于 <code>min</code> （如果 <code>min</code> 不是整数，则不小于 <code>min</code> 的向上取整数），且小于（不等于）<code>max</code>。</p>
<pre><code class="language-javascript"><code class="language-js"><span class="keyword token">function</span> <span class="function token">getRandomInt</span><span class="punctuation token">(</span>min<span class="punctuation token">,</span> max<span class="punctuation token">)</span> <span class="punctuation token">{</span>
min <span class="operator token">=</span> Math<span class="punctuation token">.</span><span class="function token">ceil</span><span class="punctuation token">(</span>min<span class="punctuation token">)</span><span class="punctuation token">;</span>
max <span class="operator token">=</span> Math<span class="punctuation token">.</span><span class="function token">floor</span><span class="punctuation token">(</span>max<span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="keyword token">return</span> Math<span class="punctuation token">.</span><span class="function token">floor</span><span class="punctuation token">(</span>Math<span class="punctuation token">.</span><span class="function token">random</span><span class="punctuation token">(</span><span class="punctuation token">)</span> <span class="operator token">*</span> <span class="punctuation token">(</span>max <span class="operator token">-</span> min<span class="punctuation token">)</span><span class="punctuation token">)</span> <span class="operator token">+</span> min<span class="punctuation token">;</span> </code>//不含最大值，含最小值<code class="language-js">
<span class="punctuation token">}</span></code></code></pre>
<p></p>
<div class="note">
<p>也许很容易想到用 <code>Math.round()</code> 来实现，但是这会导致你的随机数处于一个不均匀的分布，这可能不符合你的需求。</p>
</div>
<h3 id="得到一个两数之间的随机整数，包括两个数在内">得到一个两数之间的随机整数，包括两个数在内</h3>
<p>上一个例子提到的函数 <code>getRandomInt()</code> 结果范围包含了最小值，但不含最大值。如果你的随机结果需要同时包含最小值和最大值，怎么办呢?  <code>getRandomIntInclusive()</code> 函数可以实现。</p>
<pre><code class="language-javascript"><code class="language-js"><span class="keyword token">function</span> <span class="function token">getRandomIntInclusive</span><span class="punctuation token">(</span>min<span class="punctuation token">,</span> max<span class="punctuation token">)</span> <span class="punctuation token">{</span>
min <span class="operator token">=</span> Math<span class="punctuation token">.</span><span class="function token">ceil</span><span class="punctuation token">(</span>min<span class="punctuation token">)</span><span class="punctuation token">;</span>
max <span class="operator token">=</span> Math<span class="punctuation token">.</span><span class="function token">floor</span><span class="punctuation token">(</span>max<span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="keyword token">return</span> Math<span class="punctuation token">.</span><span class="function token">floor</span><span class="punctuation token">(</span>Math<span class="punctuation token">.</span><span class="function token">random</span><span class="punctuation token">(</span><span class="punctuation token">)</span> <span class="operator token">*</span> <span class="punctuation token">(</span>max <span class="operator token">-</span> min <span class="operator token">+</span> <span class="number token">1</span><span class="punctuation token">)</span><span class="punctuation token">)</span> <span class="operator token">+</span> min<span class="punctuation token">;</span> <span class="comment token">//含最大值，含最小值 </span>
<span class="punctuation token">}</span></code></code></pre>
<p> </p>
<h2 id="规范">规范</h2>
<p> </p>
<p> </p>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">规范版本</th>
<th scope="col">规范状态</th>
<th scope="col">注解</th>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%201st%20edition,%20June%201997.pdf" hreflang="en" lang="en" rel="noopener" title="ECMAScript 1st Edition (ECMA-262)">ECMAScript 1st Edition (ECMA-262)</a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition. JavaScript 1.0 (UNIX Only) / JavaScript 1.1 (All platforms).</td>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/5.1/#sec-15.8.2.14" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">Math.random</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td> </td>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-math.random" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Math.random</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td> </td>
</tr>
<tr>
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-math.random" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Math.random</small></a></td>
<td><span class="spec-Draft">Draft</span></td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<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>random</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">
<span>Full support</span>
</abbr>
Yes</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">
<span>Full support</span>
</abbr>
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">
<span>Full support</span>
</abbr>
1</td><td class="bc-supports-yes bc-browser-ie"><span class="bc-browser-name">IE</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
Yes</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">
<span>Full support</span>
</abbr>
Yes</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">
<span>Full support</span>
</abbr>
Yes</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">
<span>Full support</span>
</abbr>
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">
<span>Full support</span>
</abbr>
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">
<span>Full support</span>
</abbr>
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">
<span>Full support</span>
</abbr>
4</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">
<span>Full support</span>
</abbr>
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">
<span>Full support</span>
</abbr>
Yes</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">
<span>Full support</span>
</abbr>
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">
<span>Full support</span>
</abbr>
Yes</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">
<abbr class="bc-level bc-level-yes only-icon" title="Full support">
<span>Full support</span>
 
</abbr></span></dt><dd>Full support</dd></dl></section></div><p></p>
</article>
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