Revision 845707 of class expression

<div>{{Harmony}} {{jsSidebar("Operators")}}</div>

<p>The <strong>class expression</strong> is one way define a class in ECMAScript 6. Similar to <a href="/en-US/docs/Web/JavaScript/Reference/Operators/function">function expressions</a>, class expressions can be named or unnamed. If named, the name of the class is local the class body only. JavaScript classes are using prototype-based inheritance.</p>

<h2 id="Syntax">Syntax</h2>

<pre class="syntaxbox">
var MyClass = class <em>[className]</em> [extends] {
&nbsp; // class body
};</pre>

<h2 id="Description">Description</h2>

<p>A class expression has a similar syntax to a <a href="/en-US/docs/Web/JavaScript/Reference/Statements/class">class statement</a>. However, with class expressions, you are able to omit the class name ("binding identifier"), which you can't with class statements.</p>

<p>Just like with class statements, the class body of class expressions is executed in <a href="/en-US/docs/Web/JavaScript/Reference/Strict_mode">strict mode</a>.</p>

<h2 id="Examples">Examples</h2>

<h3 id="A_simple_class_expression">A simple class expression</h3>

<p>This is just a simple anonymous class expression which you can refer to using the variable "Foo".</p>

<pre class="brush: js">
var Foo = class {
  constructor() {}
  bar() {
    return "Hello World!";
  }
};

var instance = new Foo();
instance.bar(); // "Hello World!"
</pre>

<h3 id="Named_class_expressions">Named class expressions</h3>

<p>If you want to refer to the current class inside the class body, you can create a named class expression. This name is only visible in the scope of the class expression itself.</p>

<pre class="brush: js">
// TBD
var Foo = class NamedFoo {
  
}
</pre>

<h2 id="Specifications">Specifications</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('ES6', '#sec-class-definitions', 'Class definitions')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</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>{{CompatChrome(42.0)}}</td>
   <td>{{CompatNightly("firefox")}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Android Webview</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
   <th>Chrome for Android</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatChrome(42.0)}}</td>
   <td>{{CompatNightly("firefox")}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatChrome(42.0)}}</td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/function"><code>function</code> expression</a></li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/class"><code>class</code> statement</a></li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Classes">Classes</a></li>
</ul>