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+---
+title: Number.prototype.toExponential()
+slug: Web/JavaScript/Reference/Global_Objects/Number/toExponential
+translation_of: Web/JavaScript/Reference/Global_Objects/Number/toExponential
+---
+<div>{{JSRef("Global_Objects", "Number")}}</div>
+
+<h2 id="Summary" name="Summary">概述</h2>
+
+<p><strong><code>toExponential()</code></strong> 方法以指数表示法返回该数值字符串表示形式。</p>
+
+<h2 id="Syntax" name="Syntax">语法</h2>
+
+<pre class="syntaxbox"><code><em>numObj</em>.toExponential(<em>fractionDigits</em>)</code></pre>
+
+<h3 id="Parameter" name="Parameter">参数</h3>
+
+<dl>
+ <dt>fractionDigits</dt>
+ <dd>可选。一个整数,用来指定小数点后有几位数字。默认情况下用尽可能多的位数来显示数字。</dd>
+</dl>
+
+<h3 id="Returns" name="Returns">返回值</h3>
+
+<p>一个用幂的形式 (科学记数法) 来表示{{jsxref("Number")}} 对象的字符串。小数点后以fractionDigits 提供的值来四舍五入。如果 <code>fractionDigits</code> 参数被忽略了,小数点后的将尽可能用最多的位数来表示该数值。</p>
+
+<p>对数值字面量使用 <code>toExponential()</code> 方法,且该数值没有小数点和指数时,应该在该数值与该方法之间隔开一个空格,以避免点号被解释为一个小数点。也可以使用两个点号调用该方法。</p>
+
+<p>如果一个数值的小数位数多余 <code>fractionDigits</code> 参数所提供的,则该数值将会在 <code>fractionDigits</code> 指定的小数位数处四舍五入。可以查看 {{jsxref("Number.toFixed", "toFixed()")}} 方法描述中关于四舍五入的讨论,同样应用于 <code>toExponential() </code>方法。</p>
+
+<h3 id="Throws" name="Throws">异常</h3>
+
+<dl>
+ <dt>{{jsxref("Global_Objects/RangeError", "RangeError")}}</dt>
+ <dd>如果 <em>fractionDigits</em> 太小或太大将会抛出该错误。介于 0 和 20(包括20)之间的值不会引起 <code>RangeError</code> 。 执行环境也可以支持更大或更小范围。</dd>
+</dl>
+
+<dl>
+ <dt>{{jsxref("Global_Objects/TypeError", "TypeError")}}</dt>
+ <dd>如果该方法在一个非数值类型对象上调用。</dd>
+</dl>
+
+<h2 id="Example" name="Example">示例</h2>
+
+<pre class="brush:js">var numObj = 77.1234;
+
+alert("numObj.toExponential() is " + numObj.toExponential()); //输出 7.71234e+1
+
+alert("numObj.toExponential(4) is " + numObj.toExponential(4)); //输出 7.7123e+1
+
+alert("numObj.toExponential(2) is " + numObj.toExponential(2)); //输出 7.71e+1
+
+alert("77.1234.toExponential() is " + 77.1234.toExponential()); //输出 7.71234e+1
+
+alert("77 .toExponential() is " + 77 .toExponential()); //输出 7.7e+1</pre>
+
+<h2 id="规范">规范</h2>
+
+<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>ECMAScript 3rd Edition. Implemented in JavaScript 1.5</td>
+ <td>Standard</td>
+ <td>Initial definition.</td>
+ </tr>
+ <tr>
+ <td>{{SpecName('ES5.1', '#sec-15.7.4.6', 'Number.prototype.toExponential')}}</td>
+ <td>{{Spec2('ES5.1')}}</td>
+ <td> </td>
+ </tr>
+ <tr>
+ <td>{{SpecName('ES6', '#sec-number.prototype.toexponential', 'Number.prototype.toExponential')}}</td>
+ <td>{{Spec2('ES6')}}</td>
+ <td> </td>
+ </tr>
+ </tbody>
+</table>
+
+<h2 id="浏览器兼容性">浏览器兼容性</h2>
+
+<p>{{ CompatibilityTable() }}</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>{{ CompatVersionUnknown() }}</td>
+ <td>{{ CompatVersionUnknown() }}</td>
+ <td>{{ CompatVersionUnknown() }}</td>
+ <td>{{ CompatVersionUnknown() }}</td>
+ <td>{{ CompatVersionUnknown() }}</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>{{ CompatVersionUnknown() }}</td>
+ <td>{{ CompatVersionUnknown() }}</td>
+ <td>{{ CompatVersionUnknown() }}</td>
+ <td>{{ CompatVersionUnknown() }}</td>
+ <td>{{ CompatVersionUnknown() }}</td>
+ <td>{{ CompatVersionUnknown() }}</td>
+ </tr>
+ </tbody>
+</table>
+</div>
+
+<h2 id="See_Also" name="See_Also">相关链接</h2>
+
+<ul>
+ <li>{{jsxref("Number.prototype.toFixed()")}}</li>
+ <li>{{jsxref("Number.prototype.toPrecision()")}}</li>
+ <li>{{jsxref("Number.prototype.toString()")}}</li>
+</ul>