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117 lines
5.9 KiB
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<article id="wikiArticle">
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<div></div>
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<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>
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<ul>
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<li>can be exactly represented as an IEEE-754 double precision number, and</li>
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<li>whose IEEE-754 representation cannot be the result of rounding any other integer to fit the IEEE-754 representation.</li>
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</ul>
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<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>
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<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>
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<h2 id="Syntax" name="Syntax">语法</h2>
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<pre><code class="language-javascript"><code>Number.isSafeInteger(<var>testValue</var>)</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><var>testValue</var></code></dt>
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<dd>需要检测的参数。</dd>
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</dl>
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<h3 id="返回值">返回值</h3>
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<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>
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<h2 id="Example" name="Example">示例</h2>
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<pre><code class="language-js">Number.isSafeInteger(3); // true
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Number.isSafeInteger(Math.pow(2, 53)) // false
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Number.isSafeInteger(Math.pow(2, 53) - 1) // true
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Number.isSafeInteger(NaN); // false
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Number.isSafeInteger(Infinity); // false
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Number.isSafeInteger("3"); // false
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Number.isSafeInteger(3.1); // false
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Number.isSafeInteger(3.0); // true
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</code></pre>
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<h2 id="Polyfill">Polyfill</h2>
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<pre><code>Number.isSafeInteger = Number.isSafeInteger || function (value) {
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return Number.isInteger(value) && Math.abs(value) <= Number.MAX_SAFE_INTEGER;
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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">Specification</th>
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<th scope="col">Status</th>
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<th scope="col">Comment</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-number.issafeinteger" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Number.isSafeInteger</small></a></td>
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<td><span class="spec-Standard">Standard</span></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://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>
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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="Browser_compatibility" name="Browser_compatibility">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><a href="/en-US/Firefox/Releases/32" title="Released on 2014-09-02.">32</a> (32)</td>
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<td><span style="color: #f00;">未实现</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>10.0</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: #f00;">未实现</span></td>
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<td><span style="color: #f00;">未实现</span></td>
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<td>32.0 (32)</td>
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<td><span style="color: #f00;">未实现</span></td>
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<td><span style="color: #f00;">未实现</span></td>
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<td><span style="color: #f00;">未实现</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="相关链接">相关链接</h2>
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<ul>
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<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>
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<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>
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<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>
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</ul>
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</article> |