ArrayBuffer.transfer

这是一个实验中的功能

此功能某些浏览器尚在开发中，请参考浏览器兼容性表格以得到在不同浏览器中适合使用的前缀。由于该功能对应的标准文档可能被重新修订，所以在未来版本的浏览器中该功能的语法和行为可能随之改变。

静态ArrayBuffer.transfer()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。

语法

ArrayBuffer.transfer(oldBuffer [, newByteLength]

参数

oldBuffer 要转移的ArrayBuffer对象。

返回值

一个新的ArrayBuffer对象。

描述

ArrayBuffer.transfer()方法允许你增长和移除 ArrayBuffer 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。

示例

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

Polyfill

通过在脚本的开头插入以下代码, 可以部分地解决这一问题, 允许开发者在不支持它的实现中使用transfer () 的大部分功能。虽然这样调用 API不会完全实现其全部功能 , 但它依然可以将数据从一个 ArrayBuffer 传输到另一个 ArrayBuffer。

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)
            }
        }
    };
}

规范

Not part of any current specification draft document, but has been proposed for a future ECMA-262 edition.

浏览器兼容性

Feature	Chrome	Edge	Firefox (Gecko)	Internet Explorer	Opera	Safari
Basic support	No support	(Yes)	Nightly build	No support	No support	No support

Feature	Android	Chrome for Android	Edge	Firefox Mobile (Gecko)	IE Mobile	Opera Mobile	Safari Mobile
Basic support	No support	No support	(Yes)	Nightly build	No support	No support	No support