TypedArray

TypedArray 物件表示了一個底層 ArrayBuffer 的類陣列（array-like）視圖，它能以限定的型別解讀、修改 ArrayBuffer。但並沒有名為 TypedArray 的內建物件，TypedArray 也不存在可直接呼叫的建構式。真正能夠使用的是幾個原型繼承自 TypedArray 的內建物件，它們可以建立限定成員型別的物件實體來操作 ArrayBuffer。這些 TypedArray 型別的物件僅為視圖，並不會存放資料，所有的資料皆實際儲存於 ArrayBuffer 物件當中。以下將說明每種限定成員型別之 TypedArray 的共同屬性與方法。

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

語法

new TypedArray(length);
new TypedArray(typedArray);
new TypedArray(object);
new TypedArray(buffer [, byteOffset [, length]]);

where TypedArray() is one of:

Int8Array();
Uint8Array();
Uint8ClampedArray();
Int16Array();
Uint16Array();
Int32Array();
Uint32Array();
Float32Array();
Float64Array();

參數

length

When called with a length argument, a typed array containing length zeroes is created.

typedArray

When called with a typedArray argument, which can be an object of any of the typed array types (such as Int32Array), the typedArray gets copied into a new typed array. Each value in typedArray is converted to the corresponding type of the constructor before being copied into the new array.

object

When called with an object argument, a new typed array is created as if by the TypedArray.from() method.

buffer, byteOffset, length

When called with a buffer, and optionally a byteOffset and a length argument, a new typed array view is created that views the specified ArrayBuffer. The byteOffset and length parameters specify the memory range that will be exposed by the typed array view.  If both are omitted, all of buffer is viewed; if only length is omitted, the remainder of buffer is viewed.

說明

ECMAScript 2015 defines a TypedArray constructor that serves as the [[Prototype]] of all TypedArray constructors.  This constructor is not directly exposed: there is no global %TypedArray% or TypedArray property.  It is only directly accessible through Object.getPrototypeOf(Int8Array) and similar.  All TypedArrays constructors inherit common properties from the %TypedArray% constructor function.  Additionally, all typed array prototypes (TypedArray.prototype) have %TypedArray%.prototype as their [[Prototype]].

The %TypedArray% constructor on its own is not particularly useful.  Calling it or using it in a new expression will throw a TypeError, except when used during object creation in JS engines that support subclassing.  There are at present no such engines, so %TypedArray% is only useful to polyfill functions or properties onto all TypedArray constructors.

When creating an instance of a TypedArray (e.g. Int8Array), an array buffer is created internally in memory or, if an ArrayBuffer object is given as constructor argument, then this is used instead.  The buffer address is saved as an internal property of the instance and all the methods of %TypedArray%.prototype, i.e. set value and get value etc., operate on that array buffer address.

Property access

You can reference elements in the array using standard array index syntax (that is, using bracket notation). However, getting or setting indexed properties on typed arrays will not search in the prototype chain for this property, even when the indices are out of bound. Indexed properties will consult the ArrayBuffer and will never look at object properties. You can still use named properties, just like with all objects.

// Setting and getting using standard array syntax
var int16 = new Int16Array(2);
int16[0] = 42;
console.log(int16[0]); // 42

// Indexed properties on prototypes are not consulted (Fx 25)
Int8Array.prototype[20] = 'foo';
(new Int8Array(32))[20]; // 0
// even when out of bound
Int8Array.prototype[20] = 'foo';
(new Int8Array(8))[20]; // undefined
// or with negative integers
Int8Array.prototype[-1] = 'foo';
(new Int8Array(8))[-1]; // undefined

// Named properties are allowed, though (Fx 30)
Int8Array.prototype.foo = 'bar';
(new Int8Array(32)).foo; // "bar"

TypedArray 物件

屬性

TypedArray.BYTES_PER_ELEMENT

Returns a number value of the element size for the different typed array objects.

TypedArray.length

Length property whose value is 0.

TypedArray.name

Returns the string value of the constructor name. E.g "Int8Array".

get TypedArray[@@species]

The constructor function that is used to create derived objects.

TypedArray.prototype

Prototype for the TypedArray objects.

方法

TypedArray.from()

Creates a new typed array from an array-like or iterable object. See also Array.from().

TypedArray.of()

Creates a new typed array with a variable number of arguments. See also Array.of().

TypedArray 原型

All TypedArrays inherit from TypedArray.prototype.

屬性

TypedArray.BYTES_PER_ELEMENT

Returns a number value of the element size for the different TypedArray objects.

TypedArray.length

Length property, whose value is 3.

TypedArray.name

Returns the string value of the constructor name (e.g, "Int8Array").

get TypedArray[@@species]

The constructor function used to create derived objects.

TypedArray.prototype

Prototype for TypedArray objects.

方法

TypedArray.from()

Creates a new TypedArray from an array-like or iterable object. See also Array.from().

TypedArray.of()

Creates a new TypedArray with a variable number of arguments. See also Array.of().

Methods Polyfill

Many of the methods used in Typed Arrays can be polyfilled using the methods present in regular Javascript Arrays. The following snippet of JavaScript demonstrates how you might polyfill any missing Typed Array methods.

var typedArrayTypes = [Int8Array, Uint8Array, Uint8ClampedArray, Int16Array,
          Uint16Array, ​​​Int32Array, Uint32Array, ​​​Float32Array, Float64Array];

for (var k in typedArrayTypes)
    for (var v in Array.prototype)
        if (Array.prototype.hasOwnProperty(v) && 
          !typedArrayTypes[k].prototype.hasOwnProperty(v))
            typedArrayTypes[k].prototype[v] = Array.prototype[v];

規範

瀏覽器相容性

相容性備註

Starting with ECMAScript 2015, TypedArray constructors require to be constructed with a new operator. Calling a TypedArray constructor as a function without new, will throw a TypeError from now on.

var dv = Int8Array([1, 2, 3]);
// TypeError: calling a builtin Int8Array constructor 
// without new is forbidden

var dv = new Int8Array([1, 2, 3]);

參見

• JavaScript typed arrays
• ArrayBuffer
• DataView