---
title: Range.startOffset
slug: Web/API/Range/startOffset
tags:
  - API
  - DOM
  - Range
  - 属性
translation_of: Web/API/Range/startOffset
---
<p>{{ ApiRef("Range") }}</p>

<p><code><strong>Range.startOffset</strong></code> <span style="line-height: 1.5;">是一个只读属性，</span>用于返回一个表示<span style="line-height: 1.5;"> </span><code style="font-style: normal; line-height: 1.5;">Range</code><span style="line-height: 1.5;"> 在 </span><code style="font-style: normal; line-height: 1.5;">startContainer</code><span style="line-height: 1.5;"> 中的起始位置的数字。</span></p>

<p>如果 <code>startContainer</code> 是一个文本（{{domxref("Text")}}）、注释（{{domxref("Comment")}}）或者CDATA区块（{{domxref("CDATASection")}}）节点，那么返回的偏移量是从<span style="line-height: 1.5;"> </span><code style="font-style: normal; line-height: 1.5;">startContainer</code><span style="line-height: 1.5;"> 开始到 </span><span style="line-height: 1.5;">{{domxref("Range")}} 的</span><span style="line-height: 1.5;">边界点的字符数量</span><span style="line-height: 1.5;">。对于其他的节点类型，</span><span style="line-height: 1.5;"> </span><code style="font-style: normal; line-height: 1.5;">startOffset</code><span style="line-height: 1.5;"> 返回</span><span style="line-height: 1.5;"> </span><code style="font-style: normal; line-height: 1.5;">startContainer</code><span style="line-height: 1.5;"> 到边界点的子节点数量。</span></p>

<p><span style="line-height: 1.5;">可使用{{domxref("Range.setStart")}} 方法</span>改变<span style="line-height: 1.5;"> </span><code style="font-style: normal; line-height: 1.5;">Range</code><span style="line-height: 1.5;"> </span>的<span style="line-height: 1.5;"> </span><code style="font-style: normal; line-height: 1.5;">startOffset</code><span style="line-height: 1.5;"> 位置。</span></p>

<h2 id="Syntax" name="Syntax">语法</h2>

<pre class="syntaxbox"><em>startRangeOffset</em> = <em>range</em>.startOffset;
</pre>

<h2 id="Example" name="Example">示例</h2>

<pre class="brush: js">range = document.createRange();
range.setStart(startNode,startOffset);
range.setEnd(endNode,endOffset);
startRangeOffset = range.startOffset;
</pre>

<h2 id="Specification" name="Specification">规范</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">规范</th>
   <th scope="col">状态</th>
   <th scope="col">注释</th>
  </tr>
  <tr>
   <td>{{SpecName('DOM WHATWG', '#dom-range-startoffset', 'Range.startOffset')}}</td>
   <td>{{Spec2('DOM WHATWG')}}</td>
   <td>无变化</td>
  </tr>
  <tr>
   <td>{{SpecName('DOM2 Traversal_Range', 'ranges.html#Level-2-Range-attr-startOffset', 'Range.startOffset')}}</td>
   <td>{{Spec2('DOM2 Traversal_Range')}}</td>
   <td>初始规范</td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<p>{{Compat("api.Range.startOffset")}}</p>

<h2 id="参见">参见</h2>

<div id="compat-mobile"></div>

<ul>
 <li><a href="/en-US/docs/DOM/DOM_Reference" title="/en-US/docs/DOM/DOM_Reference">The DOM interfaces index</a></li>
</ul>