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Diffstat (limited to 'files/zh-cn/web/javascript/reference/global_objects/arraybuffer')
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diff --git a/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/@@species/index.html b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/@@species/index.html new file mode 100644 index 0000000000..fe99f2b076 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/@@species/index.html @@ -0,0 +1,70 @@ +--- +title: 'get ArrayBuffer[@@species]' +slug: Web/JavaScript/Reference/Global_Objects/ArrayBuffer/@@species +tags: + - ArrayBuffer + - JavaScript + - TypedArrays + - 属性 +translation_of: Web/JavaScript/Reference/Global_Objects/ArrayBuffer/@@species +--- +<div>{{JSRef}}</div> + +<p>该 <code><strong>ArrayBuffer[@@species]</strong></code> 访问器属性会返回 <code>ArrayBuffer</code> 构造器。</p> + +<h2 id="语法">语法</h2> + +<pre class="syntaxbox">ArrayBuffer[Symbol.species] +</pre> + +<h2 id="描述">描述</h2> + +<p>这个 species 访问器属性会返回默认的 <code>ArrayBuffer</code> 构造器。子类构造器可能会覆盖它以改变构造器赋值。</p> + +<h2 id="示例">示例</h2> + +<p>返回默认的 <code>ArrayBuffer</code> 构造器：</p> + +<pre class="brush: js">ArrayBuffer[Symbol.species]; // function ArrayBuffer()</pre> + +<p>在派生集合对象中（比如你定制的 array buffer <code>MyArrayBuffer</code>），<code>MyArrayBuffer</code> species 就是 <code>MyArrayBuffer</code> 构造器。但是，你可能想要在派生类里重写它，以期返回的是父类的 <code>ArrayBuffer</code> 对象：</p> + +<pre class="brush: js">class MyArrayBuffer extends ArrayBuffer { + // Overwrite MyArrayBuffer species to the parent ArrayBuffer constructor + static get [Symbol.species]() { return ArrayBuffer; } +}</pre> + +<h2 id="规范">规范</h2> + +<table class="standard-table"> + <tbody> + <tr> + <th scope="col">Specification</th> + <th scope="col">Status</th> + <th scope="col">Comment</th> + </tr> + <tr> + <td>{{SpecName('ES6', '#sec-get-arraybuffer-@@species', 'get ArrayBuffer [ @@species ]')}}</td> + <td>{{Spec2('ES6')}}</td> + <td>Initial definition.</td> + </tr> + <tr> + <td>{{SpecName('ESDraft', '#sec-get-arraybuffer-@@species', 'get ArrayBuffer [ @@species ]')}}</td> + <td>{{Spec2('ESDraft')}}</td> + <td> </td> + </tr> + </tbody> +</table> + +<h2 id="浏览器支持">浏览器支持</h2> + + + +<p>{{Compat("javascript.builtins.ArrayBuffer.@@species")}}</p> + +<h2 id="相关">相关</h2> + +<ul> + <li>{{jsxref("ArrayBuffer")}}</li> + <li>{{jsxref("Symbol.species")}}</li> +</ul> diff --git a/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/bytelength/index.html b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/bytelength/index.html new file mode 100644 index 0000000000..af8868a563 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/bytelength/index.html @@ -0,0 +1,62 @@ +--- +title: ArrayBuffer.prototype.byteLength +slug: Web/JavaScript/Reference/Global_Objects/ArrayBuffer/byteLength +translation_of: Web/JavaScript/Reference/Global_Objects/ArrayBuffer/byteLength +--- +<div>{{JSRef}}</div> + +<p><code><strong>byteLength</strong>访问器属性</code>表示一个{{jsxref("ArrayBuffer")}} 对象的字节长度。</p> + +<div>{{EmbedInteractiveExample("pages/js/arraybuffer-bytelength.html")}}</div> + + + +<h2 id="语法">语法</h2> + +<pre class="syntaxbox"><var>arr</var>aybuffer.byteLength</pre> + +<h2 id="描述">描述</h2> + +<p>byteLength属性是一个访问器属性，它的set访问器函数是undefined，这意味着你只能读这个属性。 该值在数组创建时确定，并且不可变更。如果这个<code>ArrayBuffer</code> 被移除，则此属性返回0。</p> + +<p> </p> + +<h2 id="示例">示例</h2> + +<pre class="brush:js">var buffer = new ArrayBuffer(8); +buffer.byteLength; // 8 +</pre> + +<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('Typed Array')}}</td> + <td>{{Spec2('Typed Array')}}</td> + <td>Superseded by ECMAScript 6.</td> + </tr> + <tr> + <td>{{SpecName('ES6', '#sec-get-arraybuffer.prototype.bytelength', 'ArrayBuffer.prototype.byteLength')}}</td> + <td>{{Spec2('ES6')}}</td> + <td>Initial definition in an ECMA standard.</td> + </tr> + </tbody> +</table> + +<h2 id="浏览器兼容性">浏览器兼容性</h2> + + + +<p>{{Compat("javascript.builtins.ArrayBuffer.byteLength")}}</p> + +<h2 id="相关链接">相关链接</h2> + +<ul> + <li>{{jsxref("ArrayBuffer")}}</li> +</ul> diff --git a/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/index.html b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/index.html new file mode 100644 index 0000000000..a98aca4290 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/index.html @@ -0,0 +1,161 @@ +--- +title: ArrayBuffer +slug: Web/JavaScript/Reference/Global_Objects/ArrayBuffer +tags: + - ArrayBuffer + - JavaScript + - 构造函数 + - 类型数组 +translation_of: Web/JavaScript/Reference/Global_Objects/ArrayBuffer +--- +<div> +<p>{{JSRef}}</p> + +<p><strong><code>ArrayBuffer</code></strong> 对象用来表示通用的、固定长度的原始二进制数据缓冲区。</p> + +<p>它是一个字节数组，通常在其他语言中称为“byte array”。</p> + +<p>你不能直接操作 <code>ArrayBuffer</code> 的内容，而是要通过<a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/TypedArray">类型数组对象</a>或 {{jsxref("DataView")}} 对象来操作，它们会将缓冲区中的数据表示为特定的格式，并通过这些格式来读写缓冲区的内容。</p> +</div> + +<div>{{EmbedInteractiveExample("pages/js/arraybuffer-constructor.html")}}</div> + + + +<h2 id="语法">语法</h2> + +<pre class="syntaxbox notranslate">new ArrayBuffer(length) +</pre> + +<h3 id="参数">参数</h3> + +<dl> + <dt><code>length</code></dt> + <dd>要创建的 <code>ArrayBuffer</code> 的大小，单位为字节。</dd> +</dl> + +<h3 id="返回值">返回值</h3> + +<p>一个指定大小的 <code>ArrayBuffer</code> 对象，其内容被初始化为 0。</p> + +<h3 id="异常">异常</h3> + +<p>如果 <font face="consolas, Liberation Mono, courier, monospace"><span style="background-color: rgba(220, 220, 220, 0.5);">length</span></font> 大于 {{jsxref("Number.MAX_SAFE_INTEGER")}}（>= 2 ** 53）或为负数，则抛出一个 {{jsxref("RangeError")}} 异常。</p> + +<h2 id="描述">描述</h2> + +<p><code>ArrayBuffer</code> 构造函数用来创建一个指定字节长度的 <code>ArrayBuffer</code> 对象。</p> + +<h3 id="以现有数据获取_ArrayBuffer">以现有数据获取 ArrayBuffer</h3> + +<ul> + <li><a href="https://developer.mozilla.org/zh-CN/docs/Web/API/WindowBase64/Base64_encoding_and_decoding#Appendix.3A_Decode_a_Base64_string_to_Uint8Array_or_ArrayBuffer">从 Base64 字符串</a></li> + <li><a href="https://developer.mozilla.org/zh-CN/docs/Web/API/FileReader#readAsArrayBuffer()">从本地文件</a></li> +</ul> + +<h2 id="属性">属性</h2> + +<dl> + <dt><code>ArrayBuffer.length</code></dt> + <dd>ArrayBuffer 构造函数的 length 属性，其值为1。</dd> +</dl> + +<dl> + <dt>{{jsxref("ArrayBuffer.prototype.byteLength")}}</dt> + <dd>只读属性，表示 <code>ArrayBuffer</code> 的byte的大小，在ArrayBuffer构造完成时生成，不可改变。</dd> +</dl> + +<dl> + <dt>{{jsxref("ArrayBuffer.@@species", "get ArrayBuffer[@@species]")}}</dt> + <dd>返回 ArrayBuffer 的构造函数。</dd> + <dt>{{jsxref("ArrayBuffer.prototype")}}</dt> + <dd>通过 ArrayBuffer 的原型对象可以为所有 ArrayBuffer 对象添加属性。</dd> +</dl> + +<h2 id="方法">方法</h2> + +<dl> + <dt>{{jsxref("ArrayBuffer.isView", "ArrayBuffer.isView(arg)")}}</dt> + <dd>如果参数是 ArrayBuffer 的视图实例则返回 <code>true</code>，例如 <a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/TypedArray">类型数组对象</a> 或 {{jsxref("DataView")}} 对象；否则返回 <code>false</code>。</dd> + <dt>{{jsxref("ArrayBuffer.transfer", "ArrayBuffer.transfer(oldBuffer [, newByteLength])")}} {{experimental_inline}}</dt> + <dd> + <p>返回一个新的 ArrayBuffer 对象，其内容取自 <code>oldBuffer</code> 中的数据，并且根据 <code>newByteLength</code> 的大小对数据进行截取或补 0。</p> + </dd> +</dl> + +<h2 id="ArrayBuffer_实例">ArrayBuffer 实例</h2> + +<p>所有 <code>ArrayBuffer</code> 实例都会从 {{jsxref("ArrayBuffer.prototype")}} 继承属性和方法。</p> + +<h3 id="属性_2">属性</h3> + +<p>{{page('zh-CN/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/prototype','属性')}}</p> + +<h3 id="方法_2">方法</h3> + +<p>{{page('zh-CN/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/prototype','方法')}}</p> + +<dl> + <dt>{{jsxref("ArrayBuffer.slice()")}} {{non-standard_inline}}</dt> + <dd>和 {{jsxref("ArrayBuffer.prototype.slice()")}} 功能相同。</dd> +</dl> + +<h2 id="示例">示例</h2> + +<p>下面的例子创建了一个 8 字节的缓冲区，并使用一个 {{jsxref("Global_Objects/Int32Array", "Int32Array")}} 来引用它：</p> + +<pre class="notranslate"><code>var buffer = new ArrayBuffer(8); +var view = new Int32Array(buffer);</code> +</pre> + +<h2 id="规范">规范</h2> + +<table class="standard-table"> + <tbody> + <tr> + <th scope="col">Specification</th> + <th scope="col">Status</th> + <th scope="col">Comment</th> + </tr> + <tr> + <td>{{SpecName('Typed Array')}}</td> + <td>{{Spec2('Typed Array')}}</td> + <td>已被 ECMAScript 6 中的 ArrayBuffer 取代</td> + </tr> + <tr> + <td>{{SpecName('ES6', '#sec-arraybuffer-constructor', 'ArrayBuffer')}}</td> + <td>{{Spec2('ES6')}}</td> + <td>在 ECMA 标准中的初始定义。规定了必须通过 <code>new</code> 来调用构造函数</td> + </tr> + <tr> + <td>{{SpecName('ESDraft', '#sec-arraybuffer-constructor', 'ArrayBuffer')}}</td> + <td>{{Spec2('ESDraft')}}</td> + <td></td> + </tr> + </tbody> +</table> + +<h2 id="浏览器兼容性">浏览器兼容性</h2> + +<div class="hidden"> +<p>The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p> +</div> + +<p>{{Compat("javascript.builtins.ArrayBuffer")}}</p> + +<h2 id="兼容性提醒">兼容性提醒</h2> + +<p>从 ECMAScript 2015 开始，<code>ArrayBuffer</code> 对象需要用 {{jsxref("Operators/new", "new")}} 运算符创建。如果调用构造函数时没有使用 <code>new</code>，将会抛出 {{jsxref("TypeError")}} 异常。</p> + +<pre class="brush: js example-bad notranslate">var dv = ArrayBuffer(10); +// TypeError: calling a builtin ArrayBuffer constructor +// without new is forbidden</pre> + +<pre class="brush: js example-good notranslate">var dv = new ArrayBuffer(10);</pre> + +<h2 id="相关链接">相关链接</h2> + +<ul> + <li><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Typed_arrays">JavaScript 类型数组</a></li> + <li><a href="zh-CN/docs/Web/JavaScript/Typed_arrays" title="zh-CN/JavaScript typed arrays">{{jsxref("SharedArrayBuffer")}}</a></li> +</ul> diff --git a/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/isview/index.html b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/isview/index.html new file mode 100644 index 0000000000..2b545d9c03 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/isview/index.html @@ -0,0 +1,87 @@ +--- +title: ArrayBuffer.isView() +slug: Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView +tags: + - 类型数组 + - 缓冲区 +translation_of: Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView +--- +<div>{{JSRef}}</div> + +<p><code><strong>ArrayBuffer.isView()</strong></code> 方法用来判断传入的参数值是否是一种 <code>ArrayBuffer</code> 视图（view），比如类型化数组对象（<a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray">typed array objects</a>）或者数据视图（ {{jsxref("DataView")}}）。</p> + +<div>{{EmbedInteractiveExample("pages/js/arraybuffer-isview.html")}}</div> + + + +<h2 id="语法">语法</h2> + +<pre class="brush: js"><code>ArrayBuffer.isView(<var>value</var>)</code></pre> + +<h3 id="参数">参数</h3> + +<dl> + <dt><code>value</code></dt> + <dd>被检测的值。</dd> +</dl> + +<h3 id="返回值">返回值</h3> + +<dl> + <dt><code>true</code></dt> + <dd>如果提供的参数是一种 {{jsxref("ArrayBuffer")}} 视图；</dd> + <dt><code>false</code></dt> + <dd>提供的参数不是一种 {{jsxref("ArrayBuffer")}} 视图类型；</dd> +</dl> + +<h2 id="示例">示例</h2> + +<pre class="brush: js">ArrayBuffer.isView(); // false +ArrayBuffer.isView([]); // false +ArrayBuffer.isView({}); // false +ArrayBuffer.isView(null); // false +ArrayBuffer.isView(undefined); // false +ArrayBuffer.isView(new ArrayBuffer(10)); // false + +ArrayBuffer.isView(new Uint8Array()); // true +ArrayBuffer.isView(new Float32Array()); // true +ArrayBuffer.isView(new Int8Array(10).subarray(0, 3)); // true + +var buffer = new ArrayBuffer(2); +var dv = new DataView(buffer); +ArrayBuffer.isView(dv); // true +</pre> + +<h2 id="规范">规范</h2> + +<table class="standard-table"> + <tbody> + <tr> + <th scope="col">Specification</th> + <th scope="col">Status</th> + <th scope="col">Comment</th> + </tr> + <tr> + <td>{{SpecName('Typed Array')}}</td> + <td>{{Spec2('Typed Array')}}</td> + <td>Superseded by ECMAScript 6.</td> + </tr> + <tr> + <td>{{SpecName('ES6', '#sec-arraybuffer.isview', 'ArrayBuffer.isView')}}</td> + <td>{{Spec2('ES6')}}</td> + <td>Initial definition in an ECMA standard.</td> + </tr> + </tbody> +</table> + +<h2 id="浏览器兼容性">浏览器兼容性</h2> + + + +<p>{{Compat("javascript.builtins.ArrayBuffer.isView")}}</p> + +<h2 id="另见">另见</h2> + +<ul> + <li><a href="/en-US/docs/Web/JavaScript/Typed_arrays" title="en/JavaScript typed arrays">JavaScript typed arrays</a></li> +</ul> diff --git a/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/prototype/index.html b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/prototype/index.html new file mode 100644 index 0000000000..376e969064 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/prototype/index.html @@ -0,0 +1,63 @@ +--- +title: ArrayBuffer.prototype +slug: Web/JavaScript/Reference/Global_Objects/ArrayBuffer/prototype +tags: + - ArrayBuffer +translation_of: Web/JavaScript/Reference/Global_Objects/ArrayBuffer +--- +<div>{{JSRef}}</div> + +<p><strong><code>ArrayBuffer.prototype</code></strong><code>属性表示</code>{{jsxref("ArrayBuffer")}}对象的原型。</p> + +<div>{{js_property_attributes(0,0,0)}}</div> + +<div> </div> + +<h2 id="描述">描述</h2> + +<p>ArrayBuffer 实例继承自<code>ArrayBuffer.prototype。对所有的构造函数来说，你可以通过改变构造函数的原型对象来改变所有的ArrayBuffer实例。</code></p> + +<h2 id="属性">属性</h2> + +<dl> + <dt>ArrayBuffer.prototype.constructor</dt> + <dd>指定函数，它创建一个对象的原型。其初始值是标准ArrayBuffer内置构造函数。</dd> + <dt>{{jsxref("ArrayBuffer.prototype.byteLength")}} {{readonlyInline}}</dt> + <dd>数组的字节大小。在数组创建时确定，并且不可变更。<strong>只读</strong>。</dd> +</dl> + +<h2 id="方法">方法</h2> + +<dl> + <dt>{{jsxref("ArrayBuffer.prototype.slice()")}}</dt> + <dd>返回一个新的 <code>ArrayBuffer</code> ，它的内容是这个 <code>ArrayBuffer</code> 的字节副本，从begin（包括），到end（不包括）。如果begin或end是负数，则指的是从数组末尾开始的索引，而不是从头开始。</dd> +</dl> + +<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('ES6', '#sec-arraybuffer.prototype', 'ArrayBuffer.prototype')}}</td> + <td>{{Spec2('ES6')}}</td> + <td>初始定义</td> + </tr> + </tbody> +</table> + +<h2 id="浏览器兼容性">浏览器兼容性</h2> + + + +<p>{{Compat("javascript.builtins.ArrayBuffer.prototype")}}</p> + +<h2 id="相关链接">相关链接</h2> + +<ul> + <li>{{jsxref("ArrayBuffer")}}</li> +</ul> diff --git a/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/slice/index.html b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/slice/index.html new file mode 100644 index 0000000000..2c03d1e13c --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/slice/index.html @@ -0,0 +1,83 @@ +--- +title: ArrayBuffer.prototype.slice() +slug: Web/JavaScript/Reference/Global_Objects/ArrayBuffer/slice +translation_of: Web/JavaScript/Reference/Global_Objects/ArrayBuffer/slice +--- +<div>{{JSRef}}</div> + +<p><code><strong>slice()</strong></code>方法返回一个新的 <code>ArrayBuffer</code> ，它的内容是这个<code>ArrayBuffer的</code>字节副本，从begin（包括），到end（不包括）。</p> + +<div>{{EmbedInteractiveExample("pages/js/arraybuffer-slice.html")}}</div> + + + +<h2 id="语法">语法</h2> + +<pre class="syntaxbox">arraybuffer.slice(begin[, end])</pre> + +<h3 id="参数">参数</h3> + +<dl> + <dt><code>begin</code></dt> + <dd>从零开始的字节索引，切片从这开始。</dd> +</dl> + +<dl> + <dt><code>end</code></dt> + <dd>结束切片的字节索引。如果没指定end，新的 <code>ArrayBuffer</code> 将包含这个 <code>ArrayBuffer</code> 从头到尾的所有字节。由begin和end指定的这个范围夹在当前数组的有效索引范围内。如果新<code>ArrayBuffer</code>的长度在计算后为负，它将强制为0 。</dd> +</dl> + +<h3 id="返回值">返回值</h3> + +<p> 一个新的 <code>ArrayBuffer</code> 对象。</p> + +<h2 id="描述">描述</h2> + +<p><code>slice</code> 方法复制到但不包括由end参数指示的字节。如果begin或end是负数，则指的是从数组末尾开始的索引，而不是从头开始。</p> + +<h2 id="示例">示例</h2> + +<h3 id="复制一个_ArrayBuffer">复制一个 <code>ArrayBuffer</code></h3> + +<pre class="brush: js">var buf1 = new ArrayBuffer(8); +var buf2 = buf1.slice(0); +</pre> + +<h2 id="规范">规范</h2> + +<table class="standard-table"> + <tbody> + <tr> + <th scope="col">Specification</th> + <th scope="col">Status</th> + <th scope="col">Comment</th> + </tr> + <tr> + <td>{{SpecName('Typed Array')}}</td> + <td>{{Spec2('Typed Array')}}</td> + <td>Superseded by EMCAScript 6.</td> + </tr> + <tr> + <td>{{SpecName('ES6', '#sec-arraybuffer.prototype.slice', 'ArrayBuffer.prototype.slice')}}</td> + <td>{{Spec2('ES6')}}</td> + <td>Initial definition in an ECMA standard.</td> + </tr> + <tr> + <td>{{SpecName('ESDraft', '#sec-arraybuffer.prototype.slice', 'ArrayBuffer.prototype.slice')}}</td> + <td>{{Spec2('ESDraft')}}</td> + <td> </td> + </tr> + </tbody> +</table> + +<h2 id="浏览器兼容性">浏览器兼容性</h2> + + + +<p>{{Compat("javascript.builtins.ArrayBuffer.slice")}}</p> + +<h2 id="相关链接">相关链接</h2> + +<ul> + <li>{{jsxref("ArrayBuffer")}}</li> +</ul> diff --git a/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/transfer/index.html b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/transfer/index.html new file mode 100644 index 0000000000..cf3185f637 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/arraybuffer/transfer/index.html @@ -0,0 +1,116 @@ +--- +title: ArrayBuffer.transfer() +slug: Web/JavaScript/Reference/Global_Objects/ArrayBuffer/transfer +translation_of: Archive/Web/JavaScript/ArrayBuffer.transfer +--- +<div>{{JSRef}} {{SeeCompatTable}}</div> + +<p> 静态<code><strong>ArrayBuf</strong></code><strong>fer.transfer()</strong> 方法返回一个新的ArrayBuffer， 其内容取自oldBuffer的数据，并且根据 newByteLength 的大小来对数据进行截取或者以0扩展。 如果 newByteLength 未定义，则使用 oldBuffer 的byteLength。这个操作使得 oldBuffer 处于被移除的状态。</p> + +<h2 id="语法">语法</h2> + +<pre class="syntaxbox">ArrayBuffer.transfer(oldBuffer [, newByteLength]);</pre> + +<h3 id="参数">参数</h3> + +<dl> + <dt><code>oldBuffer</code></dt> + <dd> 要转移的{{jsxref("ArrayBuffer")}}对象。</dd> + <dt>newByteLength</dt> + <dd>新 <code>ArrayBuffer</code> 对象的字节长度。</dd> +</dl> + +<h3 id="返回值">返回值</h3> + +<p>一个新的ArrayBuffer对象。</p> + +<h2 id="描述">描述</h2> + +<p><code>ArrayBuffer.transfer()</code>方法允许你增长和移除 <code>ArrayBuffer</code> 对象。不需复制就能增长一个ArrayBuffer的功能，对于大的缓冲区来说，有速度优势 (类似realloc) 。当释放底层内存时，移除ArrayBuffer的功能给开发者提供了显式控制。这避免了必须丢弃所有引用和等待垃圾回收。</p> + +<h2 id="示例">示例</h2> + +<pre class="brush: js">var buf1 = new ArrayBuffer(40); +new Int32Array(buf1)[0] = 42; + +var buf2 = ArrayBuffer.transfer(buf1, 80); +buf1.byteLength; // 0 but if you use the polyfill then the value is still 40 +buf2.byteLength; // 80 +new Int32Array(buf2)[0]; // 42 + +var buf3 = ArrayBuffer.transfer(buf2, 0); +buf2.byteLength; // 0 but if you use the polyfill then the value is still 80 +buf3.byteLength; // 0 +</pre> + +<h2 id="Polyfill">Polyfill</h2> + +<p>You can partially work around this by inserting the following code at the beginning of your scripts, allowing use of much of the functionality of transfer<font face="Consolas, Liberation Mono, Courier, monospace">()</font> in implementations that do not natively support it. This is not the exact equivalent of this API, but this function transfers data from one ArrayBuffer to another ArrayBuffer.</p> + +<pre>if(!ArrayBuffer.transfer) { + ArrayBuffer.transfer = function (source, length) { + source = Object(source); + var dest = new ArrayBuffer(length); + if(!(source instanceof ArrayBuffer) || !(dest instanceof ArrayBuffer)) { + throw new TypeError("Source and destination must be ArrayBuffer instances"); + } + if(dest.byteLength >= source.byteLength) { + var nextOffset = 0; + var leftBytes = source.byteLength; + var wordSizes = [8, 4, 2, 1]; + wordSizes.forEach(function (_wordSize_) { + if (leftBytes >= _wordSize_) { + var done = transferWith(_wordSize_, source, dest, nextOffset, leftBytes); + nextOffset = done.nextOffset; + leftBytes = done.leftBytes; + } + }); + } + return dest; + function transferWith(wordSize, source, dest, nextOffset, leftBytes) { + var ViewClass = Uint8Array; + switch (wordSize) { + case 8: + ViewClass = Float64Array; + break; + case 4: + ViewClass = Float32Array; + break; + case 2: + ViewClass = Uint16Array; + break; + case 1: + ViewClass = Uint8Array; + break; + default: + ViewClass = Uint8Array; + break; + } + var view_source = new ViewClass(source, nextOffset, Math.trunc(leftBytes / wordSize)); + var view_dest = new ViewClass(dest, nextOffset, Math.trunc(leftBytes / wordSize)); + for(var i=0; i<view_dest.length; i++) { + view_dest[i] = view_source[i]; + } + return { + nextOffset : view_source.byteOffset + view_source.byteLength, + leftBytes : source.byteLength - (view_source.byteOffset + view_source.byteLength) + } + } + }; +}</pre> + +<h2 id="规范">规范</h2> + +<p>Not part of any current specification draft document, but <a href="https://esdiscuss.org/topic/sept-23-2014-meeting-notes">has been</a> <a href="https://gist.github.com/lukewagner/2735af7eea411e18cf20">proposed</a> for a future ECMA-262 edition.</p> + +<h2 id="浏览器兼容性">浏览器兼容性</h2> + + + +<p>{{Compat("javascript.builtins.ArrayBuffer.transfer")}}</p> + +<h2 id="相关链接">相关链接</h2> + +<ul> + <li><a href="/en-US/docs/Web/JavaScript/Typed_arrays" title="en/JavaScript typed arrays">JavaScript typed arrays</a></li> +</ul> |