uTools-Manuals/docs/javascript/Reference/Global_Objects/Number/isSafeInteger.html

<article id="wikiArticle">
<div></div>
<p><strong><code>Number.isSafeInteger()</code></strong> 方法用来判断传入的参数值是否是一个“安全整数”（safe integer）。一个安全整数是一个符合下面条件的整数：</p>
<ul>
<li>can be exactly represented as an IEEE-754 double precision number, and</li>
<li>whose IEEE-754 representation cannot be the result of rounding any other integer to fit the IEEE-754 representation.</li>
</ul>
<p>比如，<code>2<sup>53</sup> - 1</code> 是一个安全整数，它能被精确表示，在任何 IEEE-754 舍入模式（rounding mode）下，没有其他整数舍入结果为该整数。作为对比，<code>2<sup>53</sup></code> 就不是一个安全整数，它能够使用 IEEE-754 表示，但是 <code>2<sup>53</sup> + 1</code> 不能使用 IEEE-754 直接表示，在就近舍入（round-to-nearest）和向零舍入中，会被舍入为 <code>2<sup>53</sup></code>。</p>
<p>安全整数范围为 <code>-(2<sup>53</sup> - 1)到</code> <code>2<sup>53</sup> - 1 </code>之间的整数，包含 <code>-(2<sup>53</sup> - 1)和</code> <code>2<sup>53</sup> - 1</code>。</p>
<h2 id="Syntax" name="Syntax">语法</h2>
<pre><code class="language-javascript"><code>Number.isSafeInteger(<var>testValue</var>)</code></code></pre>
<h3 id="Parameters" name="Parameters">参数</h3>
<dl>
<dt><code><var>testValue</var></code></dt>
<dd>需要检测的参数。</dd>
</dl>
<h3 id="返回值">返回值</h3>
<p>一个<a href="Reference/Boolean" title="此页面仍未被本地化, 期待您的翻译!"><code>布尔值</code></a> 表示给定的值是否是一个安全整数（safe integer）。</p>
<h2 id="Example" name="Example">示例</h2>
<pre><code class="language-js">Number.isSafeInteger(3);                    // true
Number.isSafeInteger(Math.pow(2, 53))       // false
Number.isSafeInteger(Math.pow(2, 53) - 1)   // true
Number.isSafeInteger(NaN);                  // false
Number.isSafeInteger(Infinity);             // false
Number.isSafeInteger("3");                  // false
Number.isSafeInteger(3.1);                  // false
Number.isSafeInteger(3.0);                  // true
</code></pre>
<h2 id="Polyfill">Polyfill</h2>
<pre><code>Number.isSafeInteger = Number.isSafeInteger || function (value) {
   return Number.isInteger(value) &amp;&amp; Math.abs(value) &lt;= Number.MAX_SAFE_INTEGER;
};</code></code></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><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-number.issafeinteger" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Number.isSafeInteger</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition.</td>
</tr>
<tr>
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-number.issafeinteger" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Number.isSafeInteger</small></a></td>
<td><span class="spec-Draft">Draft</span></td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility" name="Browser_compatibility">浏览器兼容性</h2>
<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>.
            This compatibility table still uses the old format,
            because we haven't yet converted the data it contains.
            <strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
<div class="htab">
<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
<ul>
<li class="selected"><a>Desktop</a></li>
<li><a>Mobile</a></li>
</ul>
</div><p></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><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><a href="/en-US/Firefox/Releases/32" title="Released on 2014-09-02.">32</a> (32)</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td>10.0</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><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td>32.0 (32)</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
</tr>
</tbody>
</table>
</div>
<h2 id="相关链接">相关链接</h2>
<ul>
<li> <a href="Reference/Global_Objects/Number" title="JavaScript 的 Number 对象是经过封装的能让你处理数字值的对象。Number 对象由 Number() 构造器创建。"><code>Number</code></a></li>
<li><a href="Reference/Global_Objects/Number/MIN_SAFE_INTEGER" title="Number.MIN_SAFE_INTEGER 代表在 JavaScript中最小的安全的integer型数字 (-(253 - 1))."><code>Number.MIN_SAFE_INTEGER</code></a></li>
<li><a href="Reference/Global_Objects/Number/MAX_SAFE_INTEGER" title="Number.MAX_SAFE_INTEGER 常量表示在 JavaScript 中最大的安全整数（maxinum safe integer)（253 - 1）。"><code>Number.MAX_SAFE_INTEGER</code></a></li>
</ul>
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