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

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<h2 id="概述">概述</h2>
<p><code><strong>Number.POSITIVE_INFINITY</strong></code> 属性表示正无穷大。</p>
<p>不必创建一个 <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> 实例，可使用 <code>Number.POSITIVE_INFINITY</code> 来访问该静态属性。</p>
<p></p><table class="standard-table">
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<th class="header" colspan="2"><code>Number.POSITIVE_INFINITY</code> 属性的属性特性：</th>
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<td>writable</td>
<td>false</td>
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<td>enumerable</td>
<td>false</td>
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<td>configurable</td>
<td>false</td>
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</tbody>
</table><p></p>
<h2 id="描述">描述</h2>
<p><code>Number.POSITIVE_INFINITY</code> 的值同全局对象 <a href="Reference/Global_Objects/Infinity" title="全局属性 Infinity 是一个数值，表示无穷大。"><code>Infinity</code></a> 属性的值相同。</p>
<p>该值的表现同数学上的无穷大有点儿不同：</p>
<ul>
<li>任何正值，包括 <code>POSITIVE_INFINITY</code>，乘以 <code>POSITIVE_INFINITY</code> 为 <code>POSITIVE_INFINITY</code>。</li>
<li>任何负值，包括 <code>NEGATIVE_INFINITY</code>，乘以 <code>POSITIVE_INFINITY</code> 为 <code>NEGATIVE_INFINITY</code>。</li>
<li>0 乘以 <code>POSITIVE_INFINITY</code> 为 NaN。</li>
<li>NaN 乘以 <code>POSITIVE_INFINITY</code> 为 NaN。</li>
<li><code>POSITIVE_INFINITY</code> 除以 <code>NEGATIVE_INFINITY</code> 以外的任何负值为 <code>NEGATIVE_INFINITY</code>。</li>
<li><code>POSITIVE_INFINITY</code> 除以 <code>POSITIVE_INFINITY</code> 以外的任何正值为 <code>POSITIVE_INFINITY</code>。</li>
<li><code>POSITIVE_INFINITY</code> 除以 <code>NEGATIVE_INFINITY</code> 或 <code>POSITIVE_INFINITY</code> 为 NaN。</li>
<li>任何数除以 <code>POSITIVE_INFINITY</code> 为 0。</li>
</ul>
<p>You might use the <code>Number.POSITIVE_INFINITY</code> property to indicate an error condition that returns a finite number in case of success. Note, however, that <a href="Reference/Global_Objects/isFinite" title="该全局 isFinite() 函数用来判断被传入的参数值是否为一个有限数值（finite number）。在必要情况下，参数会首先转为一个数值。"><code>isFinite</code></a> would be more appropriate in such a case.</p>
<h2 id="示例">示例</h2>
<p>下例中，赋值给变量 <code>bigNumber</code> 一个大于 JavaScript 中最大值的值。当 <code>if</code> 语句执行时，变量 <code>bigNumber</code> 值为 "<code>Infinity</code>"， 因此在继续执行代码前，为变量 <code>bigNumber</code> 设置一个容易管理的值。</p>
<pre><code  class="language-javascript">var bigNumber = Number.MAX_VALUE * 2
if (bigNumber == Number.POSITIVE_INFINITY) {
 bigNumber = returnFinite();
}
</code></pre>
<h2 id="规范">规范</h2>
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<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
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<td>ECMAScript 1st Edition. Implemented in JavaScript 1.1</td>
<td>Standard</td>
<td>Initial definition.</td>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/5.1/#sec-15.7.3.6" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">Number.POSITIVE_INFINITY</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td> </td>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-number.positive_infinity" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Number.POSITIVE_INFINITY</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td> </td>
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</tbody>
</table>
<h2 id="浏览器兼容性">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>
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<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
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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>
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<div id="compat-mobile">
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<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>
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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>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<h2 id="See_also" name="See_also">相关链接</h2>
<ul>
<li><a href="Reference/Global_Objects/Number/NEGATIVE_INFINITY" title="Number.NEGATIVE_INFINITY 属性表示负无穷大。"><code>Number.NEGATIVE_INFINITY</code></a></li>
<li><a href="Reference/Global_Objects/Infinity" title="全局属性 Infinity 是一个数值，表示无穷大。"><code>Infinity</code></a></li>
<li><a href="Reference/Global_Objects/isFinite" title="该全局 isFinite() 函数用来判断被传入的参数值是否为一个有限数值（finite number）。在必要情况下，参数会首先转为一个数值。"><code>isFinite</code></a></li>
</ul>
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