Revision 793699 of void operator

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

<p>The <strong><code>void</code> operator</strong> evaluates the given <code><em>expression</em></code> and then returns {{jsxref("Global_Objects/undefined", "undefined")}}.</p>

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

<pre class="syntaxbox">
void <em>expression</em></pre>

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

<p>This operator allows inserting expressions that produce side effects into places where an expression that evaluates to {{jsxref("Global_Objects/undefined", "undefined")}} is desired.</p>

<p>The <code>void</code> operator is often used merely to obtain the <code>undefined</code> primitive value, usually using "<code>void(0)</code>" (which is equivalent to "<code>void 0</code>"). In these cases, the global variable {{jsxref("Global_Objects/undefined", "undefined")}} can be used instead (assuming it has not been assigned to a non-default value).</p>

<h2 id="Immediately_Invoked_Function_Expressions">Immediately Invoked Function Expressions</h2>

<p>When using an <a href="/en-US/docs/Glossary/IIFE">immediately-invoked function expression</a>, <code>void</code> can be used to force the <code>function</code> keyword to be treated as an expression instead of a declaration.</p>

<pre class="brush: js">
void function iife() {
    var bar = function () {};
    var baz = function () {};
    var foo = function () {
        bar();
        baz();
     };
    var biz = function () {};

    foo();
    biz();
}();
</pre>

<h2 id="JavaScript_URIs">JavaScript URIs</h2>

<p>When a browser follows a <code>javascript:</code> URI, it evaluates the code in the URI and then replaces the contents of the page with the returned value, unless the returned value is {{jsxref("Global_Objects/undefined", "undefined")}}. The <code>void</code> operator can be used to return {{jsxref("Global_Objects/undefined", "undefined")}}. For example:</p>

<pre class="brush: html">
&lt;a href="javascript:void(0);"&gt;
  Click here to do nothing
&lt;/a&gt;

&lt;a href="javascript:void(document.body.style.backgroundColor='green');"&gt;
  Click here for green background
&lt;/a&gt;
</pre>

<p>Note, however, that the <code>javascript:</code> pseudo protocol is discouraged over other alternatives, such as unobtrusive event handlers.</p>

<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>ECMAScript 1st Edition.</td>
   <td>Standard</td>
   <td>Initial definition. Implemented in JavaScript 1.1</td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-11.4.2', 'The void Operator')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td>&nbsp;</td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-void-operator', 'The void Operator')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>&nbsp;</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>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</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>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

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

<ul>
 <li><code><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined">undefined</a></code></li>
</ul>