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128 lines
5.6 KiB
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<article id="wikiArticle">
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<div></div>
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<div> </div>
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<p><strong><code>Math.sign()</code></strong> 函数返回一个数字的符号, 指示数字是正数，负数还是零。</p>
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<h2 id="Syntax" name="Syntax">语法</h2>
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<pre><code class="language-javascript"><code>Math.sign(<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>任意数字.</dd>
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</dl>
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<h2 id="Description" name="Description">描述</h2>
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<p>因为 <code>sign </code>是 <code>Math </code>的一个静态方法，所以你应该使用 Math.sign() ，而不是作为你创建的一个Math对象的一种方法 （Math不是一个构造函数）。</p>
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<p>而不是作为您创建的Math对象的一种方法（Math不是构造函数）。</p>
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<p>此函数共有5种返回值, 分别是<strong> 1, -1, 0, -0, NaN.</strong> 代表的各是<strong>正数, 负数, 正零, 负零, NaN</strong>。</p>
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<p>传入该函数的参数会被<strong>隐式转换</strong>成数字类型。</p>
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<h2 id="Examples" name="Examples">示例</h2>
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<h3 id="使用Math.sign()">使用Math.sign()</h3>
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<pre><code class="language-js">Math.sign(3); // 1
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Math.sign(-3); // -1
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Math.sign("-3"); // -1
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Math.sign(0); // 0
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Math.sign(-0); // -0
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Math.sign(NaN); // NaN
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Math.sign("foo"); // NaN
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Math.sign(); // NaN
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</code></pre>
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<h2 id="Compatibility" name="Compatibility">Polyfill</h2>
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<pre><code class="language-js language-js"><code class="language-js"><span class="keyword token">function</span> <span class="function token">sign<span class="punctuation token">(</span></span>x<span class="punctuation token">)</span> <span class="punctuation token">{</span>
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x <span class="operator token">=</span> <span class="operator token">+</span>x<span class="comment token"> ;// convert to a number
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</span> <span class="keyword token">if</span> <span class="punctuation token">(</span>x <span class="operator token">===</span> <span class="number token">0</span> <span class="operator token">||</span> <span class="function token">isNaN<span class="punctuation token">(</span></span>x<span class="punctuation token">)</span><span class="punctuation token">)</span>
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<span class="keyword token">return</span> x;
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<span class="keyword token">return</span> x <span class="operator token">></span> <span class="number token">0</span> <span class="operator token">?</span> <span class="number token">1</span> <span class="punctuation token">:</span> <span class="operator token">-</span><span class="number token">1;</span>
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<span class="punctuation token">}</span></code></code></pre>
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<p> </p>
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<pre><code>if (!Math.sign) {
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Math.sign = function(x) {
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// If x is NaN, the result is NaN.
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// If x is -0, the result is -0.
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// If x is +0, the result is +0.
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// If x is negative and not -0, the result is -1.
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// If x is positive and not +0, the result is +1.
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x = +x; // convert to a number
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if (x === 0 || isNaN(x)) {
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return Number(x);
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}
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return x > 0 ? 1 : -1;
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};
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}</code></code></pre>
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<p> </p>
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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-math.sign" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Math.sign</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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</tbody>
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</table>
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<h2 id="浏览器兼容性">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>38</td>
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<td><a href="/en-US/Firefox/Releases/25" title="Released on 2013-10-29.">25</a> (25)</td>
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<td><span style="color: #f00;">未实现</span></td>
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<td>25</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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<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>25.0 (25)</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="See_also" name="See_also">相关链接</h2>
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<ul>
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<li><a href="Reference/Global_Objects/Math" title="Math 是一个内置对象， 它具有数学常数和函数的属性和方法。不是一个函数对象。"><code>Math</code></a> 对象</li>
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</ul>
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</article> |