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diff --git a/files/zh-cn/web/api/textencoder/index.html b/files/zh-cn/web/api/textencoder/index.html new file mode 100644 index 0000000000..223674f74b --- /dev/null +++ b/files/zh-cn/web/api/textencoder/index.html @@ -0,0 +1,150 @@ +--- +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> |