uTools-Manuals/docs/javascript/Reference/Global_Objects/Proxy/handler/set.html

<article id="wikiArticle">
<div></div>
<p><code><strong>handler.set()</strong></code> 方法用于拦截设置属性值的操作</p>
<h2 id="语法">语法</h2>
<pre><code  class="language-javascript">var p = new Proxy(target, {
  set: function(target, property, value, receiver) {
  }
});
</code></pre>
<h3 id="参数">参数</h3>
<p>以下是传递给set方法的参数，<code>this上下文绑定在</code>handler对象上.</p>
<dl>
<dt><code>target</code></dt>
<dd>目标对象。</dd>
<dt><code>property</code></dt>
<dd>被设置的属性名。</dd>
<dt><code>value</code></dt>
<dd>被设置的新值。</dd>
<dt><code>receiver</code></dt>
<dd>最初被调用的对象。通常是proxy本身，但handler的set方法也有可能在原型链上或以其他方式被间接地调用（因此不一定是proxy本身）。</dd>
<dd>比如，假设有一段代码执行 <code>obj.name = "jen"，obj不是一个proxy且自身不含name属性，但它的原型链上有一个proxy，那么那个proxy的set拦截函数会被调用，此时obj会作为receiver参数传进来。</code></dd>
</dl>
<h3 id="返回值">返回值</h3>
<p>set方法应该返回一个布尔值，返回true代表此次设置属性成功了，如果返回false且设置属性操作发生在严格模式下，那么会抛出一个<code>TypeError</code>。</p>
<h2 id="描述">描述</h2>
<p><code><strong>handler.set</strong></code> 方法用于拦截设置属性值的操作。</p>
<h3 id="拦截">拦截</h3>
<p>该方法会拦截目标对象的以下操作:</p>
<ul>
<li>指定属性值: <code>proxy[foo] = bar</code> 和 <code>proxy.foo = bar</code></li>
<li>指定继承者的属性值: <code>Object.create(proxy)[foo] = bar</code></li>
<li><a href="Reference/Global_Objects/Reflect/set" title="静态方法 Reflect.set() 工作方式就像在一个对象上设置一个属性。"><code>Reflect.set()</code></a></li>
</ul>
<h3 id="约束">约束</h3>
<p>如果违背以下的约束条件，proxy会抛出一个<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>:</p>
<ul>
<li>若目标属性是不可写及不可配置的，则不能改变它的值。</li>
<li>如果目标属性没有配置存储方法，即set方法是undefined的，则不能设置它的值。</li>
<li>在严格模式下，若set方法返回false，则会抛出一个 <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> 异常。</li>
</ul>
<h2 id="示例">示例</h2>
<p>以下代码演示如何捕获属性的设置操作。</p>
<pre><code  class="language-javascript">var p = new Proxy({}, {
  set: function(target, prop, value, receiver) {
    console.log("called: " + prop + " = " + value);
    return true;
  }
});

p.a = 10; // "called: a = 10"
</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" href="https://www.ecma-international.org/ecma-262/6.0/#sec-proxy-object-internal-methods-and-internal-slots-set-p-v-receiver" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">[[Set]]</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition.</td>
</tr>
<tr>
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-set-p-v-receiver" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">[[Set]]</small></a></td>
<td><span class="spec-Draft">Draft</span></td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<div><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
            This compatibility table still uses the old format,
            because we haven't yet converted the data it contains.
            <strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
<div class="htab">
<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
<ul>
<li class="selected"><a>Desktop</a></li>
<li><a>Mobile</a></li>
</ul>
</div></div>
<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><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
<td><a href="/en-US/Firefox/Releases/18" title="Released on 2013-01-08.">18</a> (18)</td>
<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></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><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
<td>18.0 (18)</td>
<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
</tr>
</tbody>
</table>
</div>
<h2 id="另见">另见</h2>
<ul>
<li><a href="Reference/Global_Objects/Proxy" title="Proxy 对象用于定义基本操作的自定义行为（如属性查找，赋值，枚举，函数调用等）。"><code>Proxy</code></a></li>
<li><a href="Reference/Global_Objects/Proxy/handler" title="处理器对象用来自定义代理对象的各种可代理操作。"><code>handler</code></a></li>
<li><a href="Reference/Global_Objects/Reflect/set" title="静态方法 Reflect.set() 工作方式就像在一个对象上设置一个属性。"><code>Reflect.set()</code></a></li>
</ul>
</article>