Revision 805187 of WindowBase64.btoa()

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

<p>Creates a base-64 encoded ASCII string from a "string" of binary data.</p>

<p>Please note that this is not suitable for raw <a href="https://www.unicode.org/standard/WhatIsUnicode.html">Unicode</a> strings! See Unicode section below.</p>

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

<pre class="syntaxbox">
var encodedData = window.btoa(<em>stringToEncode</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="Notes" name="Notes">Notes</h2>

<p>You can use this method to encode data which may otherwise cause communication problems, transmit it, then use the <code>{{domxref("WindowBase64.atob","window.atob()")}}</code>&nbsp;method to decode the data again. For example, you can encode control characters such as ASCII values 0 through 31.</p>

<p><code>btoa()</code> is also available to XPCOM components implemented in JavaScript, even though <a href="/en-US/docs/DOM/window" title="DOM/window"><code>window</code></a> is not the global object in components.</p>

<h2 id="Unicode_Strings">Unicode Strings</h2>

<p>In most browsers, calling <code>window.btoa()</code>&nbsp;on a Unicode string will cause a Character Out Of Range exception.</p>

<p>To avoid this, consider this pattern, noted by <a class="external" href="https://ecmanaut.blogspot.com/2006/07/encoding-decoding-utf8-in-javascript.html" title="https://ecmanaut.blogspot.com/2006/07/encoding-decoding-utf8-in-javascript.html">Johan Sundström</a>:</p>

<pre class="brush:js">
function utf8_to_b64(str) {
    return window.btoa(unescape(encodeURIComponent(str)));
}

function b64_to_utf8(str) {
    return decodeURIComponent(escape(window.atob(str)));
}

// Usage:
utf8_to_b64('✓ à la mode'); // JTI1dTI3MTMlMjUyMCUyNUUwJTI1MjBsYSUyNTIwbW9kZQ==
b64_to_utf8('JTI1dTI3MTMlMjUyMCUyNUUwJTI1MjBsYSUyNTIwbW9kZQ=='); // "✓ à la mode"

utf8_to_b64('I \u2661 Unicode!'); // SSUyNTIwJTI1dTI2NjElMjUyMFVuaWNvZGUlMjUyMQ==
b64_to_utf8('SSUyNTIwJTI1dTI2NjElMjUyMFVuaWNvZGUlMjUyMQ=='); // "I ♡ Unicode!"

</pre>

<p>A better, more faithful and less expensive solution is to convert the <a href="/en-US/docs/Web/API/DOMString" title="/en-US/docs/Web/API/DOMString"><code>DOMString</code></a> to a UTF-8 encoded string passing for <a href="/en-US/docs/Web/JavaScript/Typed_arrays" title="/en-US/docs/Web/JavaScript/Typed_arrays">typed arrays</a>. In order to do this, please, <strong>read <a href="/en-US/docs/Web/JavaScript/Base64_encoding_and_decoding#Solution_.232_.E2.80.93_rewriting_atob()_and_btoa()_using_TypedArrays_and_UTF-8" title="/en-US/docs/Web/JavaScript/Base64_encoding_and_decoding#Solution_.232_.E2.80.93_rewriting_atob()_and_btoa()_using_TypedArrays_and_UTF-8">this paragraph</a></strong>.</p>

<h2 id="Browser_compatibility" name="Browser_compatibility">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-btoa', 'WindowBase64.btoa()')}}</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-btoa', 'WindowBase64.btoa()')}}</td>
   <td>{{Spec2('HTML5.1')}}</td>
   <td>Snapshot of {{SpecName("HTML WHATWG")}}. No change.</td>
  </tr>
  <tr>
   <td>{{SpecName("HTML5 W3C", "#dom-windowbase64-btoa", "WindowBase64.btoa()")}}</td>
   <td>{{Spec2('HTML5 W3C')}}</td>
   <td>Snapshot of {{SpecName("HTML WHATWG")}}. Creation of <code>WindowBase64</code> (properties where 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]</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>btoa()</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>

<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.atob","window.atob()")}}</li>
 <li><a href="/en-US/docs/Components.utils.importGlobalProperties">Components.utils.importGlobalProperties</a></li>
</ul>