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---
title: Кодирование и декодирование в формате Base64
slug: Glossary/Base64
translation_of: Glossary/Base64
original_slug: Web/API/WindowBase64/Base64_encoding_and_decoding
---
<p><strong>Base64</strong> - это группа схожих <a href="https://en.wikipedia.org/wiki/Binary-to-text_encoding">binary-to-text encoding</a> схем, которые представляют двоичные данные в ASCII-формате методом перевода в radix-64 представление. Термин <em>Base64</em> происходит от a specific <a href="https://en.wikipedia.org/wiki/MIME#Content-Transfer-Encoding">MIME content transfer encoding</a>.</p>
<p>Кодирование Base64 широко используется в случаях, когда требуется перекодировать двоичные данные для передачи по каналу приспособленному для передачи текстовых данных. Это делается с целью защиты двоичных данных от любых возможных повреждений при передаче. Base64 широко используется во многих приложениях, включая электронную почту (<a href="https://en.wikipedia.org/wiki/MIME">MIME</a>), и при сохранении больших объёмов данных в <a href="/en-US/docs/XML">XML</a>.</p>
<p>В языке JavaScript существуют две функции, для кодирования и декодирования данных в/из формат Base64 соответственно:</p>
<ul>
<li>{{domxref("WindowBase64.btoa","btoa()")}}</li>
<li>{{domxref("WindowBase64.atob","atob()")}}</li>
</ul>
<p><code><font face="Arial, x-locale-body, sans-serif"><span style="background-color: #ffffff;">Функция </span></font>atob()</code> декодирует Base64-кодированную строку. В противоположность ей, функция <code>btoa()</code> создаёт Base64 кодированную ASCII строку из "строки" бинарных данных.</p>
<p>Обе функции <code>atob()</code> и <code>btoa()</code> работают со строками. Если вам необходимо работать с <a href="/en-US/docs/Web/API/ArrayBuffer"><code>ArrayBuffers</code></a>, обратитесь к <a href="#">этому параграфу</a>.</p>
<table class="topicpage-table">
<tbody>
<tr>
<td>
<h2 class="Documentation" id="Documentation" name="Documentation">Документация</h2>
<dl>
<dt><a href="https://developer.mozilla.org/en-US/docs/data_URIs" title="https://developer.mozilla.org/en-US/docs/data_URIs"><code>data</code> URIs</a></dt>
<dd><small><code>data</code> URIs, описанные в <a class="external" href="http://tools.ietf.org/html/rfc2397">RFC 2397</a>, позволяют создателям контента встроить в документ маленькие файлы в виде строки (инлайном).</small></dd>
<dt><a href="https://en.wikipedia.org/wiki/Base64">Base64</a></dt>
<dd><small>Wikipedia article about Base64 encoding.</small></dd>
<dt>{{domxref("WindowBase64.atob","atob()")}}</dt>
<dd><small>Decodes a string of data which has been encoded using base-64 encoding.</small></dd>
<dt>{{domxref("WindowBase64.btoa","btoa()")}}</dt>
<dd><small>Creates a base-64 encoded ASCII string from a "string" of binary data.</small></dd>
<dt><a href="#The_Unicode_Problem">The "Unicode Problem"</a></dt>
<dd><small>In most browsers, calling <code>btoa()</code> on a Unicode string will cause a <code>Character Out Of Range</code> exception. This paragraph shows some solutions.</small></dd>
<dt><a href="/en-US/docs/URIScheme" title="/en-US/docs/URIScheme">URIScheme</a></dt>
<dd><small>List of Mozilla supported URI schemes</small></dd>
<dt><a href="/en-US/docs/Web/JavaScript/Typed_arrays/StringView" title="/en-US/docs/Web/JavaScript/Typed_arrays/StringView"><code>StringView</code></a></dt>
<dd>In this article is published a library of ours whose aims are:
<ul>
<li>creating a <a class="external" href="http://en.wikipedia.org/wiki/C_%28programming_language%29">C</a>-like interface for strings (i.e. array of characters codes —<a href="/en-US/docs/Web/JavaScript/Typed_arrays/ArrayBufferView" title="/en-US/docs/Web/JavaScript/Typed_arrays/ArrayBufferView"> <code>ArrayBufferView</code></a> in JavaScript) based upon the JavaScript <a href="/en-US/docs/Web/JavaScript/Typed_arrays/ArrayBuffer" title="/en-US/docs/Web/JavaScript/Typed_arrays/ArrayBuffer"><code>ArrayBuffer</code></a> interface,</li>
<li>creating a collection of methods for such string-like objects (since now: <code>stringView</code>s) which work <strong>strictly on array of numbers</strong> rather than on immutable JavaScript strings,</li>
<li>working with other Unicode encodings, different from default JavaScript's UTF-16 <a href="/en-US/docs/Web/API/DOMString" title="/en-US/docs/Web/API/DOMString"><code>DOMString</code></a>s,</li>
</ul>
</dd>
</dl>
</td>
<td>
<h2 class="Tools" id="Tools" name="Tools">Tools</h2>
<ul>
<li><a href="#Solution_2_–_rewrite_the_DOMs_atob()_and_btoa()_using_JavaScript's_TypedArrays_and_UTF-8">Rewriting <code>atob()</code> and <code>btoa()</code> using <code>TypedArray</code>s and UTF-8</a></li>
<li><a href="/en-US/docs/Web/JavaScript/Typed_arrays/StringView" title="/en-US/docs/Web/JavaScript/Typed_arrays/StringView"><code>StringView</code> – a C-like representation of strings based on typed arrays</a></li>
</ul>
<h2 class="Related_Topics" id="Related_Topics" name="Related_Topics">Related Topics</h2>
<ul>
<li><a href="/en-US/docs/Web/JavaScript/Typed_arrays/ArrayBuffer"><code>ArrayBuffer</code></a></li>
<li><a href="/en-US/docs/Web/JavaScript/Typed_arrays">Typed arrays</a></li>
<li><code><a href="/en-US/docs/Web/JavaScript/Typed_arrays/ArrayBufferView">ArrayBufferView</a></code></li>
<li><a href="/en-US/docs/Web/JavaScript/Typed_arrays/Uint8Array"><code>Uint8Array</code></a></li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays/StringView" title="/en-US/docs/Web/JavaScript/Typed_arrays/StringView"><code>StringView</code> – a C-like representation of strings based on typed arrays</a></li>
<li><a href="/en-US/docs/Web/API/DOMString" title="/en-US/docs/Web/API/DOMString"><code>DOMString</code></a></li>
<li><a href="/en-US/docs/URI" title="/en-US/docs/URI"><code>URI</code></a></li>
<li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURI" title="/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURI"><code>encodeURI()</code></a></li>
</ul>
</td>
</tr>
</tbody>
</table>
<h2 id="The_Unicode_Problem">The "Unicode Problem"</h2>
<p>Since <a href="/en-US/docs/Web/API/DOMString" title="/en-US/docs/Web/API/DOMString"><code>DOMString</code></a>s are 16-bit-encoded strings, in most browsers calling <code>window.btoa</code> on a Unicode string will cause a <code>Character Out Of Range</code> exception if a character exceeds the range of a 8-bit byte (0x00~0xFF). There are two possible methods to solve this problem:</p>
<ul>
<li>the first one is to escape the whole string (with UTF-8, see {{jsxref("encodeURIComponent")}}) and then encode it;</li>
<li>the second one is to convert the UTF-16 <a href="/en-US/docs/Web/API/DOMString" title="/en-US/docs/Web/API/DOMString"><code>DOMString</code></a> to an UTF-8 array of characters and then encode it.</li>
</ul>
<p>Here are the two possible methods.</p>
<h3 id="Solution_1_–_escaping_the_string_before_encoding_it">Solution #1 – escaping the string before encoding it</h3>
<pre class="brush:js">function b64EncodeUnicode(str) {
// first we use encodeURIComponent to get percent-encoded UTF-8,
// then we convert the percent encodings into raw bytes which
// can be fed into btoa.
return btoa(encodeURIComponent(str).replace(/%([0-9A-F]{2})/g,
function toSolidBytes(match, p1) {
return String.fromCharCode('0x' + p1);
}));
}
b64EncodeUnicode('✓ à la mode'); // "4pyTIMOgIGxhIG1vZGU="
b64EncodeUnicode('\n'); // "Cg=="
</pre>
<p>To decode the Base64-encoded value back into a String:</p>
<pre class="brush: js">function b64DecodeUnicode(str) {
// Going backwards: from bytestream, to percent-encoding, to original string.
return decodeURIComponent(atob(str).split('').map(function(c) {
return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
}).join(''));
}
b64DecodeUnicode('4pyTIMOgIGxhIG1vZGU='); // "✓ à la mode"
b64DecodeUnicode('Cg=='); // "\n"
</pre>
<p><a href="https://github.com/coolaj86/unibabel-js">Unibabel</a> implements common conversions using this strategy.</p>
<h3 id="Solution_2_–_rewrite_the_DOMs_atob_and_btoa_using_JavaScripts_TypedArrays_and_UTF-8">Solution #2 – rewrite the DOMs <code>atob()</code> and <code>btoa()</code> using JavaScript's <code>TypedArray</code>s and UTF-8</h3>
<p>Use a <a href="/en-US/docs/Web/API/TextEncoder">TextEncoder</a> polyfill such as <a href="https://github.com/inexorabletash/text-encoding">TextEncoding</a> (also includes legacy windows, mac, and ISO encodings), <a href="https://github.com/coolaj86/TextEncoderLite">TextEncoderLite</a>, combined with a <a href="https://github.com/feross/buffer">Buffer</a> and a Base64 implementation such as <a href="https://github.com/beatgammit/base64-js">base64-js</a>.</p>
<p>When a native <code>TextEncoder</code> implementation is not available, the most light-weight solution would be to use <a href="https://github.com/coolaj86/TextEncoderLite">TextEncoderLite</a> with <a href="https://github.com/beatgammit/base64-js">base64-js</a>. Use the browser implementation when you can.</p>
<p>The following function implements such a strategy. It assumes base64-js imported as <code><script type="text/javascript" src="base64js.min.js"/></code>. Note that TextEncoderLite only works with UTF-8.</p>
<pre class="brush: js">function Base64Encode(str, encoding = 'utf-8') {
var bytes = new (TextEncoder || TextEncoderLite)(encoding).encode(str);
return base64js.fromByteArray(bytes);
}
function Base64Decode(str, encoding = 'utf-8') {
var bytes = base64js.toByteArray(str);
return new (TextDecoder || TextDecoderLite)(encoding).decode(bytes);
}
</pre>
|
