Revision 805189 of WindowBase64.atob()

<p name="Summary">{{APIRef("HTML DOM")}}</p>

<p>The <strong><code>WindowBase64.atob()</code></strong>&nbsp;function decodes a string of data which has been encoded using base-64 encoding. You can use the {{domxref("WindowBase64.btoa","window.btoa()")}} method to encode and transmit data which may otherwise cause communication problems, then transmit it and use the <code>window.atob()</code> method to decode the data again. For example, you can encode, transmit, and decode control characters such as ASCII values 0 through 31.</p>

<p>For use with Unicode or UTF-8 strings, see <a href="/en-US/docs/Web/JavaScript/Base64_encoding_and_decoding#The_.22Unicode_Problem.22">this note at Base64 encoding and decoding</a> and <a href="/en-US/docs/Web/API/window.btoa#Unicode_Strings">this note at <code>window.btoa()</code></a>.</p>

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

<pre class="syntaxbox">
var decodedData = window.atob(<em>encodedData</em>);</pre>

<h2 id="Example" name="Example">Example</h2>

<pre class="brush:js">
var encodedData = window.btoa("Hello, world"); // encode a string
var decodedData = window.atob(encodedData); // decode the string</pre>

<h2 id="Specifications">Specifications</h2>

<table class="standard-table">
 <thead>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td>{{SpecName('HTML WHATWG', '#dom-windowbase64-atob', 'WindowBase64.atob()')}}</td>
   <td>{{Spec2('HTML WHATWG')}}</td>
   <td>No change since the latest snapshot, {{SpecName("HTML5.1")}}.</td>
  </tr>
  <tr>
   <td>{{SpecName('HTML5.1', '#dom-windowbase64-atob', 'WindowBase64.atob()')}}</td>
   <td>{{Spec2('HTML5.1')}}</td>
   <td>Snapshot of {{SpecName("HTML WHATWG")}}. No change.</td>
  </tr>
  <tr>
   <td>{{SpecName("HTML5 W3C", "#dom-windowbase64-atob", "WindowBase64.atob()")}}</td>
   <td>{{Spec2('HTML5 W3C')}}</td>
   <td>Snapshot of {{SpecName("HTML WHATWG")}}. Creation of <code>WindowBase64</code> (properties were on the target before it).</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility" name="Browser_compatibility">Browser compatibility</h2>

<div>{{CompatibilityTable}}</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 (WebKit)</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatGeckoDesktop(1)}}[1][2]</td>
   <td>10</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>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>{{CompatGeckoMobile(1)}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

<p>[1]&nbsp; <code>atob()</code> is also available to XPCOM components implemented in JavaScript, even though <code><a href="/en-US/docs/DOM/window">window</a></code> is not the global object in components.</p>

<p>[2] Starting with <a href="/en-US/Firefox/Releases/27/Site_Compatibility">Firefox&nbsp;27</a>, this <code>atob()</code>&nbsp;method ignores all space characters in the argument to comply with the latest HTML5 spec. ({{ bug(711180) }})</p>

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

<ul>
 <li><a href="/Web/API/WindowBase64/Base64_encoding_and_decoding">Base64 encoding and decoding</a></li>
 <li><a href="/en-US/docs/data_URIs"><code>data</code> URIs</a></li>
 <li>{{domxref("WindowBase64.btoa","window.btoa()")}}</li>
 <li><a href="/en-US/docs/Components.utils.importGlobalProperties">Components.utils.importGlobalProperties</a></li>
</ul>