---
title: TextEncoder
slug: Web/API/TextEncoder
tags:
- API
- 参考
- 接口
- 编码
translation_of: Web/API/TextEncoder
---
<div>{{APIRef("Encoding API")}}</div>
<p><code><strong>TextEncoder</strong></code> 接受代码点流作为输入，并提供 UTF-8 字节流作为输出。</p>
<div class="blockIndicator note">
<p><strong>Note</strong>: There is a polyfill implementation to support non-UTF-8 text encodings on <a href="https://github.com/inexorabletash/text-encoding">GitHub</a>.</p>
</div>
<h2 id="例子">例子</h2>
<pre class="brush: js; notranslate">const encoder = new TextEncoder()
const view = encoder.encode('€')
console.log(view); // Uint8Array(3) [226, 130, 172]
</pre>
<h2 id="构造器">构造器</h2>
<dl>
<dt>{{domxref("TextEncoder.TextEncoder", "TextEncoder()")}}</dt>
<dd>返回一个新构造的 <code>TextEncoder</code>，它默认使用 UTF-8 编码将代码点流转换成字节流。</dd>
</dl>
<h2 id="属性">属性</h2>
<p><em><code>TextEncoder</code> 接口不继承任何属性。</em></p>
<dl>
<dt>{{domxref("TextEncoder.encoding")}} {{readonlyInline}}</dt>
<dd>总是返回 "<code>utf-8</code>"。</dd>
</dl>
<h2 id="方法">方法</h2>
<p><em><code>TextEncoder</code> 接口不继承任何方法。</em></p>
<dl>
<dt>{{domxref("TextEncoder.encode()")}}</dt>
<dd>接受一个 {{domxref("USVString")}} 作为输入，返回一个包含文本的 {{jsxref("Uint8Array")}}，其中的文本使用 UTF-8 编码。</dd>
<dt>{{DOMxRef("TextEncoder.prototype.encodeInto()")}}</dt>
<dd>接受一个 {{domxref("USVString")}} 作为输入、一个{{jsxref("Uint8Array")}} 作为输出目标，返回一个指示编码进度的目录（dictionary）对象。此方法的性能可能回比更早出现的 <code>encode()</code> 方法好一些。</dd>
</dl>
<h2 id="Polyfill">Polyfill</h2>
<p>The below polyfill is compliant with the standard and therefore only supports UTF-8. It is designed to work in IE5 "out of the box". However, in IE5-IE9, it will return a regular Array instead of a TypedArray. In those cases a polyfill might be impractical for large strings. Finally, note that you should run the below code through a minifier (especially closure compiler) to turn sequences like <code>0x1e << 3</code> into <code>0xf0</code>. These sequences are not already precomputed because they serve to aesthetically illustrate how the polyfill works.</p>
<pre class="brush: js notranslate">if (typeof TextEncoder === "undefined") {
TextEncoder=function TextEncoder(){};
TextEncoder.prototype.encode = function encode(str) {
"use strict";
var Len = str.length, resPos = -1;
// The Uint8Array's length must be at least 3x the length of the string because an invalid UTF-16
// takes up the equivelent space of 3 UTF-8 characters to encode it properly. However, Array's
// have an auto expanding length and 1.5x should be just the right balance for most uses.
var resArr = typeof Uint8Array === "undefined" ? new Array(Len * 1.5) : new Uint8Array(Len * 3);
for (var point=0, nextcode=0, i = 0; i !== Len; ) {
point = str.charCodeAt(i), i += 1;
if (point >= 0xD800 && point <= 0xDBFF) {
if (i === Len) {
resArr[resPos += 1] = 0xef/*0b11101111*/; resArr[resPos += 1] = 0xbf/*0b10111111*/;
resArr[resPos += 1] = 0xbd/*0b10111101*/; break;
}
// https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
nextcode = str.charCodeAt(i);
if (nextcode >= 0xDC00 && nextcode <= 0xDFFF) {
point = (point - 0xD800) * 0x400 + nextcode - 0xDC00 + 0x10000;
i += 1;
if (point > 0xffff) {
resArr[resPos += 1] = (0x1e/*0b11110*/<<3) | (point>>>18);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | ((point>>>12)&0x3f/*0b00111111*/);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | ((point>>>6)&0x3f/*0b00111111*/);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | (point&0x3f/*0b00111111*/);
continue;
}
} else {
resArr[resPos += 1] = 0xef/*0b11101111*/; resArr[resPos += 1] = 0xbf/*0b10111111*/;
resArr[resPos += 1] = 0xbd/*0b10111101*/; continue;
}
}
if (point <= 0x007f) {
resArr[resPos += 1] = (0x0/*0b0*/<<7) | point;
} else if (point <= 0x07ff) {
resArr[resPos += 1] = (0x6/*0b110*/<<5) | (point>>>6);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | (point&0x3f/*0b00111111*/);
} else {
resArr[resPos += 1] = (0xe/*0b1110*/<<4) | (point>>>12);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | ((point>>>6)&0x3f/*0b00111111*/);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | (point&0x3f/*0b00111111*/);
}
}
if (typeof Uint8Array !== "undefined") return resArr.subarray(0, resPos + 1);
// else // IE 6-9
resArr.length = resPos + 1; // trim off extra weight
return resArr;
};
TextEncoder.prototype.toString = function(){return "[object TextEncoder]"};
try { // Object.defineProperty only works on DOM prototypes in IE8
Object.defineProperty(TextEncoder.prototype,"encoding",{
get:function(){if(TextEncoder.prototype.isPrototypeOf(this)) return"utf-8";
else throw TypeError("Illegal invocation");}
});
} catch(e) { /*IE6-8 fallback*/ TextEncoder.prototype.encoding = "utf-8"; }
if(typeof Symbol!=="undefined")TextEncoder.prototype[Symbol.toStringTag]="TextEncoder";
}
</pre>
<p><small>Source: <a href="https://github.com/anonyco/FastestSmallestTextEncoderDecoder" rel="noopener">https://github.com/anonyco/FastestSmallestTextEncoderDecoder</a></small></p>
<h2 id="规范">规范</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">规范</th>
<th scope="col">状态</th>
<th scope="col">备注</th>
</tr>
<tr>
<td>{{SpecName('Encoding', '#interface-textencoder', 'TextEncoder')}}</td>
<td>{{Spec2('Encoding')}}</td>
<td>Initial definition.</td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<p>{{Compat("api.TextEncoder")}}</p>
<h2 id="参见">参见</h2>
<ul>
<li>The {{DOMxRef("TextDecoder")}} interface describing the inverse operation.</li>
<li><a href="/en-US/Add-ons/Code_snippets/StringView" title="/en-US/docs/Web/JavaScript/Typed_arrays/StringView"><code>StringView</code></a> – a C-like representation of strings based on typed arrays</li>
<li>A <a href="https://github.com/inexorabletash/text-encoding" title="http://code.google.com/p/stringencoding/">shim</a> allowing to use this interface in browsers that don't support it.</li>
<li><code><a href="/en-US/docs/Mozilla/Tech/XPCOM/Language_Bindings/Components.utils.importGlobalProperties">Components.utils.importGlobalProperties</a></code></li>
<li><a href="https://nodejs.org/api/util.html#util_class_util_textencoder">Node.js supports global export from v11.0.0</a></li>
</ul>