uTools-Manuals/docs/javascript/Reference/Global_Objects/Atomics/compareExchange.html

<article id="wikiArticle">
<div> <div class="blockIndicator experimental indicator-warning">
<p><span title="这是一个实验性的 API，请尽量不要在生产环境中使用它。"><i class="icon-beaker"> </i></span> <strong>这是一个实验中的功能</strong><br/>此功能某些浏览器尚在开发中，请参考<a href="#Browser_compatibility">浏览器兼容性表格</a>以得到在不同浏览器中适合使用的前缀。由于该功能对应的标准文档可能被重新修订，所以在未来版本的浏览器中该功能的语法和行为可能随之改变。</p>
</div></div>
<p><code><strong>Atomics</strong></code><strong><code>.compareExchange()</code></strong> 静态方法会在数组的值与期望值相等的时候，将给定的替换值替换掉数组上的值，然后返回旧值。此原子操作保证在写上修改的值之前不会发生其他写操作。</p>
<div><iframe class="interactive interactive-js" frameborder="0" height="250" src="https://interactive-examples.mdn.mozilla.net/pages/js/atomics-compareexchange.html" width="100%"></iframe></div>
<p class="hidden">The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone <a class="external" href="https://github.com/mdn/interactive-examples" rel="noopener">https://github.com/mdn/interactive-examples</a> and send us a pull request.</p>
<h2 id="语法">语法</h2>
<pre><code class="language-javascript">Atomics.compareExchange(typedArray, index, expectedValue, replacementValue)
</code></pre>
<h3 id="参数">参数</h3>
<dl>
<dt><code>typedArray</code></dt>
<dd>一个共享的整型 typed array。例如 <a href="Reference/Global_Objects/Int8Array" title="Int8Array 类型数组表示二进制补码8位有符号整数的数组。内容初始化为0。 一旦建立，你可以使用对象的方法引用数组中的元素，或使用标准数组索引语法( 即，使用括号注释)。"><code>Int8Array</code></a>，<a href="Reference/Global_Objects/Uint8Array" title="Uint8Array 数组类型表示一个8位无符号整型数组，创建时内容被初始化为0。创建完后，可以以对象的方式或使用数组下标索引的方式引用数组中的元素。"><code>Uint8Array</code></a>，<a href="Reference/Global_Objects/Int16Array" title="The Int16Array typed array represents an array of twos-complement 16-bit signed integers in the platform byte order. If control over byte order is needed, use DataView instead. The contents are initialized to 0. Once established, you can reference elements in the array using the object's methods, or using standard array index syntax (that is, using bracket notation)."><code>Int16Array</code></a>，<a href="Reference/Global_Objects/Uint16Array" title="The Uint16Array typed array represents an array of 16-bit unsigned integers in the platform byte order. If control over byte order is needed, use DataView instead. The contents are initialized to 0. Once established, you can reference elements in the array using the object's methods, or using standard array index syntax (that is, using bracket notation)."><code>Uint16Array</code></a>，<a href="Reference/Global_Objects/Int32Array" title="The Int32Array typed array represents an array of twos-complement 32-bit signed integers in the platform byte order. If control over byte order is needed, use DataView instead. The contents are initialized to 0. Once established, you can reference elements in the array using the object's methods, or using standard array index syntax (that is, using bracket notation)."><code>Int32Array</code></a>，或 <a href="Reference/Global_Objects/Uint32Array" title="Uint32Array表示一个由基于平台字节序的32位无符号字节组成的数组.如果需要对字节顺序进行控制(译者注:即 littleEndian 或 bigEndian),请使用DataView代替.数组中每个元素的初始值都是0.一旦创建，你可以用对象的方法引用数组里的元素，或者使用标准的数组索引语法（即，使用中括号）。"><code>Uint32Array</code></a>。</dd>
<dt><code>index</code></dt>
<dd><code>typedArray</code> 的索引。</dd>
<dt><code>expectedValue</code></dt>
<dd>用于比较的值。</dd>
<dt>replacementValue</dt>
<dd>将要替换上的值。</dd>
</dl>
<h3 id="返回值">返回值</h3>
<p>给定位置的旧值(<code>typedArray[index]</code>).</p>
<h3 id="错误">错误</h3>
<ul>
<li>假如 <code>typedArray</code> 不是允许的整型之一，则抛出 <a href="Reference/Global_Objects/TypeError" title="TypeError（类型错误） 对象用来表示值的类型非预期类型时发生的错误。"><code>TypeError</code></a>。</li>
<li><code><font face="Open Sans, Arial, sans-serif">假如 </font>typedArray</code> 不是一个贡献的 typed array，则抛出 <a href="Reference/Global_Objects/TypeError" title="TypeError（类型错误） 对象用来表示值的类型非预期类型时发生的错误。"><code>TypeError</code></a>。</li>
<li>如果 <code>index</code> 超出了 <code>typedArray 的边界，则抛出</code> <a href="Reference/Global_Objects/RangeError" title="RangeError对象标明一个错误，当一个值不在其所允许的范围或者集合中。"><code>RangeError</code></a>。</li>
</ul>
<h2 id="示例">示例</h2>
<pre><code  class="language-javascript">var sab = new SharedArrayBuffer(1024);
var ta = new Uint8Array(sab);
ta[0] = 7;

Atomics.compareExchange(ta, 0, 7, 12); // returns 7, the old value
Atomics.load(ta, 0); // 12</code></pre>
<h2 id="规范">规范</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><a class="external" hreflang="en" lang="en">Unknown<br/><small lang="zh-CN">Atomics.compareExchange</small></a></td>
<td><span class="spec-">Unknown</span></td>
<td>Initial definition.</td>
</tr>
</tbody>
</table>
<h2 id="浏览器支持">浏览器支持</h2>
<div class="hidden">The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out <a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</div>
<p></p><div class="bc-data"><a class="bc-github-link external" href="https://github.com/mdn/browser-compat-data" rel="noopener">Update compatibility data on GitHub</a><table class="bc-table bc-table-js"><thead><tr class="bc-platforms"><td></td><th class="bc-platform-desktop" colspan="6"><span>Desktop</span></th><th class="bc-platform-mobile" colspan="7"><span>Mobile</span></th><th class="bc-platform-server" colspan="1"><span>Server</span></th></tr><tr class="bc-browsers"><td></td><th class="bc-browser-chrome"><span class="bc-head-txt-label bc-head-icon-chrome">Chrome</span></th><th class="bc-browser-edge"><span class="bc-head-txt-label bc-head-icon-edge">Edge</span></th><th class="bc-browser-firefox"><span class="bc-head-txt-label bc-head-icon-firefox">Firefox</span></th><th class="bc-browser-ie"><span class="bc-head-txt-label bc-head-icon-ie">Internet Explorer</span></th><th class="bc-browser-opera"><span class="bc-head-txt-label bc-head-icon-opera">Opera</span></th><th class="bc-browser-safari"><span class="bc-head-txt-label bc-head-icon-safari">Safari</span></th><th class="bc-browser-webview_android"><span class="bc-head-txt-label bc-head-icon-webview_android">Android webview</span></th><th class="bc-browser-chrome_android"><span class="bc-head-txt-label bc-head-icon-chrome_android">Chrome for Android</span></th><th class="bc-browser-edge_mobile"><span class="bc-head-txt-label bc-head-icon-edge_mobile">Edge Mobile</span></th><th class="bc-browser-firefox_android"><span class="bc-head-txt-label bc-head-icon-firefox_android">Firefox for Android</span></th><th class="bc-browser-opera_android"><span class="bc-head-txt-label bc-head-icon-opera_android">Opera for Android</span></th><th class="bc-browser-safari_ios"><span class="bc-head-txt-label bc-head-icon-safari_ios">Safari on iOS</span></th><th class="bc-browser-samsunginternet_android"><span class="bc-head-txt-label bc-head-icon-samsunginternet_android">Samsung Internet</span></th><th class="bc-browser-nodejs"><span class="bc-head-txt-label bc-head-icon-nodejs">Node.js</span></th></tr></thead><tbody><tr><th scope="row"><code>compareExchange</code></th><td class="bc-supports-yes bc-browser-chrome bc-has-history"><span class="bc-browser-name">Chrome</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              68<div class="bc-icons"></div><section class="bc-history" id="sect1"><dl><dt class="bc-supports-yes bc-supports"><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              68<div class="bc-icons"></div></dt><dd></dd><dt class="bc-supports-no bc-supports"><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>60 — 63<div class="bc-icons"><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> </div></dt><dd><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> Chrome disabled <code>SharedArrayBuffer</code> on January 5, 2018 to help reduce the efficacy of <a class="external" href="https://www.chromium.org/Home/chromium-security/ssca" rel="noopener">speculative side-channel attacks</a>. This was a temporary removal while mitigations were put in place.</dd></dl></section></td><td class="bc-supports-no bc-browser-edge bc-has-history"><span class="bc-browser-name">Edge</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>16 — 17<div class="bc-icons"><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> </div><section class="bc-history" id="sect2"><dl><dt class="bc-supports-no bc-supports"><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>16 — 17<div class="bc-icons"><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> </div></dt><dd><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> Support was removed to mitigate <a class="external" href="https://blogs.windows.com/msedgedev/2018/01/03/speculative-execution-mitigations-microsoft-edge-internet-explorer" rel="noopener">speculative execution side-channel attacks (Windows blog)</a>.</dd></dl></section></td><td class="bc-supports-yes bc-browser-firefox bc-has-history"><span class="bc-browser-name">Firefox</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              57<div class="bc-icons"><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> <abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> </div><section class="bc-history" id="sect3"><dl><dt class="bc-supports-yes bc-supports"><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              57<div class="bc-icons"><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> <abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> </div></dt><dd><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> Support was disabled by default to mitigate <a class="external" href="https://blog.mozilla.org/security/2018/01/03/mitigations-landing-new-class-timing-attack/" rel="noopener">speculative execution side-channel attacks (Mozilla Security Blog)</a>.</dd><dd><abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> From version 57: this feature is behind the <code>javascript.options.shared_memory</code> preference (needs to be set to <code>true</code>). To change preferences in Firefox, visit about:config.</dd><dt class="bc-supports-no bc-supports"><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>55 — 57<div class="bc-icons"></div></dt><dd></dd><dt class="bc-supports-no bc-supports"><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>46 — 55<div class="bc-icons"><abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> </div></dt><dd><abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> From version 46 until version 55 (exclusive): this feature is behind the <code>javascript.options.shared_memory</code> preference (needs to be set to <code>true</code>). To change preferences in Firefox, visit about:config.</dd></dl></section></td><td class="bc-supports-no bc-browser-ie"><span class="bc-browser-name">IE</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</td><td class="bc-supports-no bc-browser-opera"><span class="bc-browser-name">Opera</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</td><td class="bc-supports-no bc-browser-safari"><span class="bc-browser-name">Safari</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>10.1 — ?</td><td class="bc-supports-no bc-browser-webview_android bc-has-history"><span class="bc-browser-name">WebView Android</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>60 — 63<div class="bc-icons"><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> </div><section class="bc-history" id="sect4"><dl><dt class="bc-supports-no bc-supports"><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>60 — 63<div class="bc-icons"><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> </div></dt><dd><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> Chrome disabled <code>SharedArrayBuffer</code> on January 5, 2018 to help reduce the efficacy of <a class="external" href="https://www.chromium.org/Home/chromium-security/ssca" rel="noopener">speculative side-channel attacks</a>. This is intended as a temporary measure until other mitigations are in place.</dd></dl></section></td><td class="bc-supports-no bc-browser-chrome_android bc-has-history"><span class="bc-browser-name">Chrome Android</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>60 — 63<div class="bc-icons"><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> </div><section class="bc-history" id="sect5"><dl><dt class="bc-supports-no bc-supports"><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>60 — 63<div class="bc-icons"><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> </div></dt><dd><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> Chrome disabled <code>SharedArrayBuffer</code> on January 5, 2018 to help reduce the efficacy of <a class="external" href="https://www.chromium.org/Home/chromium-security/ssca" rel="noopener">speculative side-channel attacks</a>. This is intended as a temporary measure until other mitigations are in place.</dd></dl></section></td><td class="bc-supports-unknown bc-browser-edge_mobile"><span class="bc-browser-name">Edge Mobile</span><abbr title="Compatibility unknown; please update this.">
                ?
              </abbr></td><td class="bc-supports-yes bc-browser-firefox_android bc-has-history"><span class="bc-browser-name">Firefox Android</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              57<div class="bc-icons"><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> <abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> </div><section class="bc-history" id="sect6"><dl><dt class="bc-supports-yes bc-supports"><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              57<div class="bc-icons"><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> <abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> </div></dt><dd><abbr class="only-icon" title="See implementation notes"><span>Notes</span><i class="ic-footnote"></i></abbr> Support was disabled by default to mitigate <a class="external" href="https://blog.mozilla.org/security/2018/01/03/mitigations-landing-new-class-timing-attack/" rel="noopener">speculative execution side-channel attacks (Mozilla Security Blog)</a>.</dd><dd><abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> From version 57: this feature is behind the <code>javascript.options.shared_memory</code> preference (needs to be set to <code>true</code>). To change preferences in Firefox, visit about:config.</dd><dt class="bc-supports-no bc-supports"><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>55 — 57<div class="bc-icons"></div></dt><dd></dd><dt class="bc-supports-no bc-supports"><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>46 — 55<div class="bc-icons"><abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> </div></dt><dd><abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> From version 46 until version 55 (exclusive): this feature is behind the <code>javascript.options.shared_memory</code> preference (needs to be set to <code>true</code>). To change preferences in Firefox, visit about:config.</dd></dl></section></td><td class="bc-supports-no bc-browser-opera_android"><span class="bc-browser-name">Opera Android</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</td><td class="bc-supports-no bc-browser-safari_ios"><span class="bc-browser-name">Safari iOS</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</td><td class="bc-supports-no bc-browser-samsunginternet_android"><span class="bc-browser-name">Samsung Internet Android</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</td><td class="bc-supports-yes bc-browser-nodejs"><span class="bc-browser-name">nodejs</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              8.10.0</td></tr></tbody></table><section class="bc-legend" id="sect7"><h3 class="offscreen" id="Legend">Legend</h3><dl><dt><span class="bc-supports-yes bc-supports">
<abbr class="bc-level bc-level-yes only-icon" title="Full support">
<span>Full support</span>
                  
                </abbr></span></dt><dd>Full support</dd><dt><span class="bc-supports-no bc-supports">
<abbr class="bc-level bc-level-no only-icon" title="No support">
<span>No support</span>
                  
                </abbr></span></dt><dd>No support</dd><dt><span class="bc-supports-unknown bc-supports">
<abbr class="bc-level bc-level-unknown only-icon" title="Compatibility unknown">
<span>Compatibility unknown</span>
                  
                </abbr></span></dt><dd>Compatibility unknown</dd><dt><abbr class="only-icon" title="See implementation notes."><span>See implementation notes.</span><i class="ic-footnote"></i></abbr></dt><dd>See implementation notes.</dd><dt><abbr class="only-icon" title="User must explicitly enable this feature."><span>User must explicitly enable this feature.</span><i class="ic-disabled"></i></abbr></dt><dd>User must explicitly enable this feature.</dd></dl></section></div><p></p>
<h2 id="相关">相关</h2>
<ul>
<li><a href="Reference/Global_Objects/Atomics" title="Atomics 对象提供了一组静态方法用来对 SharedArrayBuffer 对象进行原子操作。"><code>Atomics</code></a></li>
<li><a href="Reference/Global_Objects/Atomics/exchange" title="Atomics.exchange() 静态方法会用给定的值替换掉数组上的值，然后返回数组的旧值。此原子操作保证在写上修改的值之前不会发生其他写操作。"><code>Atomics.exchange()</code></a></li>
</ul>
</article>