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+---
+title: new.target
+slug: Web/JavaScript/Reference/Operators/new.target
+tags:
+  - Classes
+  - ECMAScript 2015
+  - JavaScript
+  - Reference
+translation_of: Web/JavaScript/Reference/Operators/new.target
+---
+<div>{{JSSidebar("Operators")}}</div>
+
+<div><strong><code>new.target</code></strong>属性允许你检测函数或构造方法是否是通过<a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/new">new</a>运算符被调用的。在通过<a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/new">new</a>运算符被初始化的函数或构造方法中，<code>new.target</code>返回一个指向构造方法或函数的引用。在普通的函数调用中，<code>new.target</code> 的值是{{jsxref("undefined")}}。</div>
+
+<h2 id="语法">语法</h2>
+
+<pre class="syntaxbox">new.target</pre>
+
+<h2 id="描述">描述</h2>
+
+<p><code>new.target</code>语法由一个关键字"<code>new</code>"，一个点，和一个属性名"<font face="Consolas, Liberation Mono, Courier, monospace">target</font>"组成。通常"<code>new.</code>"<code>的</code>作用是提供属性访问的上下文，但这里"<code>new.</code>"其实不是一个真正的对象。不过在构造方法调用中，<code>new.target</code>指向被<code>new</code>调用的构造函数，所以"<code>new.</code>"成为了一个虚拟上下文。</p>
+
+<p><code>new.target</code>属性适用于所有函数访问的元属性。在  <a href="http://www.javascripttutorial.net/es6/javascript-arrow-function/">arrow functions</a> 中，<code>new.target</code> 指向最近的外层函数的<code>new.target</code>（An arrow function expression does not have its own this, arguments, super , or new.target) 。</p>
+
+<h2 id="示例">示例</h2>
+
+<h3 id="函数调用中的_new.target">函数调用中的 new.target</h3>
+
+<p>在普通的函数调用中（和作为构造函数来调用相对），<code>new.target</code>的值是{{jsxref("undefined")}}。这使得你可以检测一个函数是否是作为构造函数通过<a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/new">new</a>被调用的。</p>
+
+<pre class="brush: js">function Foo() {
+  if (!new.target) throw "Foo() must be called with new";
+  console.log("Foo instantiated with new");
+}
+
+Foo(); // throws "Foo() must be called with new"
+new Foo(); // logs "Foo instantiated with new"
+</pre>
+
+<h3 id="构造方法中的_new.target">构造方法中的 new.target</h3>
+
+<p>在类的构造方法中，<code>new.target</code>指向直接被<code>new</code>执行的构造函数。并且当一个父类构造方法在子类构造方法中被调用时，情况与之相同。</p>
+
+<pre class="brush: js">class A {
+  constructor() {
+    console.log(new.target.name);
+  }
+}
+
+class B extends A { constructor() { super(); } }
+
+var a = new A(); // logs "A"
+var b = new B(); // logs "B"
+
+class C { constructor() { console.log(new.target); } }
+class D extends C { constructor() { super(); } }
+
+var c = new C(); // logs class C{constructor(){console.log(new.target);}}
+var d = new D(); // logs class D extends C{constructor(){super();}}
+</pre>
+
+<p class="summary">从上面类 C 和 D 的例子可以看出来，new.target 指向的是初始化类的类定义。比如当 D 通过 new 初始化的时候，打印出了 D 的类定义，C 的例子与之类似，打印出的是 C 的类定义。</p>
+
+<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>{{SpecName('ES2015', '#sec-built-in-function-objects', 'Built-in Function Objects')}}</td>
+   <td>{{Spec2('ES2015')}}</td>
+   <td>Initial definition.</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#sec-built-in-function-objects', 'Built-in Function Objects')}}</td>
+   <td>{{Spec2('ESDraft')}}</td>
+   <td> </td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="浏览器兼容">浏览器兼容</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 href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</div>
+
+<p>{{Compat("javascript.operators.new_target")}}</p>
+
+<h2 id="相关链接">相关链接</h2>
+
+<ul>
+ <li><a href="/zh-CN/docs/Web/JavaScript/Reference/Functions">Functions</a></li>
+ <li><a href="/zh-CN/docs/Web/JavaScript/Reference/Classes">Classes</a></li>
+ <li><code><a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/new">new</a></code></li>
+ <li><code><a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/this">this</a></code></li>
+</ul>