diff options
Diffstat (limited to 'files/zh-cn/web/javascript/reference/global_objects/number/toexponential/index.html')
-rw-r--r-- | files/zh-cn/web/javascript/reference/global_objects/number/toexponential/index.html | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/files/zh-cn/web/javascript/reference/global_objects/number/toexponential/index.html b/files/zh-cn/web/javascript/reference/global_objects/number/toexponential/index.html new file mode 100644 index 0000000000..a19013e4c4 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/number/toexponential/index.html @@ -0,0 +1,142 @@ +--- +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> |