---
title: CanvasRenderingContext2D.textAlign
slug: Web/API/CanvasRenderingContext2D/textAlign
translation_of: Web/API/CanvasRenderingContext2D/textAlign
---
<div>{{APIRef}}</div>

<p><code><strong>CanvasRenderingContext2D</strong></code><strong><code>.textAlign</code></strong> 是 Canvas 2D API 描述绘制文本时，文本的对齐方式的属性。注意，该对齐是基于CanvasRenderingContext2D.fillText方法的x的值。所以如果textAlign="center"，那么该文本将画在 x-50%*width。</p>

<blockquote>
<p>译者注：这里的textAlign="center"比较特殊。textAlign的值为center时候文本的居中是基于你在fillText的时候所给的x的值，也就是说文本一半在x的左边，一半在x的右边（可以理解为计算x的位置时从默认文字的左端，改为文字的中心，因此你只需要考虑x的位置即可）。所以，如果你想让文本在整个canvas居中，就需要将fillText的x值设置成canvas的宽度的一半。</p>
</blockquote>

<h2 id="语法">语法</h2>

<pre class="syntaxbox"><var><em>ctx</em>.textAlign = "left" || "right" || "center" || "start" || "end";</var>
</pre>

<h3 id="选项">选项</h3>

<p>有效值：</p>

<dl>
 <dt>left</dt>
 <dd>文本左对齐。</dd>
 <dt>right</dt>
 <dd>文本右对齐。</dd>
 <dt>center</dt>
 <dd>文本居中对齐。</dd>
 <dt>start</dt>
 <dd>文本对齐界线开始的地方 （左对齐指本地从左向右，右对齐指本地从右向左）。</dd>
 <dt>end</dt>
 <dd>文本对齐界线结束的地方 （左对齐指本地从左向右，右对齐指本地从右向左）。</dd>
</dl>

<p>默认值是 <code>start。</code></p>

<blockquote>
<p><code>译者注：direction属性会对此属性产生影响。如果direction属性设置为ltr，则left和start的效果相同，right和end的效果相同；如果direction属性设置为rtl，则left和end的效果相同，right和start的效果相同。</code></p>
</blockquote>

<h2 id="示例">示例</h2>

<h3 id="Using_the_textAlign_property" name="Using_the_textAlign_property">使用 <code>textAlign</code> 属性</h3>

<p>这是一段简单的代码片段，使用 <code>textAlign</code> 属性设置文本的不同对齐方式。</p>

<h4 id="HTML">HTML</h4>

<pre class="brush: html">&lt;canvas id="canvas"&gt;&lt;/canvas&gt;
</pre>

<h4 id="JavaScript">JavaScript</h4>

<pre class="brush: js">var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

ctx.font = "48px serif";
ctx.textAlign = "left";
ctx.strokeText("Hello world", 0, 100);
</pre>

<p>修改下面的代码并在线查看 canvas 的变化：</p>

<div class="hidden">
<h6 id="Playable_code" name="Playable_code">Playable code</h6>

<pre class="brush: html">&lt;canvas id="canvas" width="400" height="200" class="playable-canvas"&gt;&lt;/canvas&gt;
&lt;div class="playable-buttons"&gt;
  &lt;input id="edit" type="button" value="Edit" /&gt;
  &lt;input id="reset" type="button" value="Reset" /&gt;
&lt;/div&gt;
&lt;textarea id="code" class="playable-code"&gt;
ctx.font = "48px serif";
ctx.textAlign = "left";
ctx.strokeText("Hello world", 0, 100);&lt;/textarea&gt;
</pre>

<pre class="brush: js">var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;

function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}

reset.addEventListener("click", function() {
  textarea.value = code;
  drawCanvas();
});

edit.addEventListener("click", function() {
  textarea.focus();
})

textarea.addEventListener("input", drawCanvas);
window.addEventListener("load", drawCanvas);
</pre>
</div>

<p>{{ EmbedLiveSample('Playable_code', 700, 360) }}</p>

<h2 id="规范描述">规范描述</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('HTML WHATWG', "scripting.html#dom-context-2d-textalign", "CanvasRenderingContext2D.textAlign")}}</td>
   <td>{{Spec2('HTML WHATWG')}}</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>{{ CompatGeckoDesktop("1.9.1") }}</td>
   <td>{{ CompatIE(9) }}</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>{{ CompatGeckoMobile("1.9.1") }}</td>
   <td>{{ CompatVersionUnknown() }}</td>
   <td>{{ CompatVersionUnknown() }}</td>
   <td>{{ CompatVersionUnknown() }}</td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="参见">参见</h2>

<ul>
 <li>接口定义， {{domxref("CanvasRenderingContext2D")}}.</li>
</ul>