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 containinglength
zeroes is created. - typedArray
- When called with a
typedArray
argument, which can be an object of any of the typed array types (such asInt32Array
), thetypedArray
gets copied into a new typed array. Each value intypedArray
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 theTypedArray.from()
method. - buffer, byteOffset, length
- When called with a
buffer
, and optionally abyteOffset
and alength
argument, a new typed array view is created that views the specifiedArrayBuffer
. ThebyteOffset
andlength
parameters specify the memory range that will be exposed by the typed array view. If both are omitted, all ofbuffer
is viewed; if onlylength
is omitted, the remainder ofbuffer
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
Type | Value Range | Size in bytes | Description | Web IDL type | Equivalent C type |
Int8Array |
-128 to 127 | 1 | 8-bit two's complement signed integer | byte |
int8_t |
Uint8Array |
0 to 255 | 1 | 8-bit unsigned integer | octet |
uint8_t |
Uint8ClampedArray |
0 to 255 | 1 | 8-bit unsigned integer (clamped) | octet |
uint8_t |
Int16Array |
-32768 to 32767 | 2 | 16-bit two's complement signed integer | short |
int16_t |
Uint16Array |
0 to 65535 | 2 | 16-bit unsigned integer | unsigned short |
uint16_t |
Int32Array |
-2147483648 to 2147483647 | 4 | 32-bit two's complement signed integer | long |
int32_t |
Uint32Array |
0 to 4294967295 | 4 | 32-bit unsigned integer | unsigned long |
uint32_t |
Float32Array |
1.2x10-38 to 3.4x1038 | 4 | 32-bit IEEE floating point number ( 7 significant digits e.g. 1.1234567) | unrestricted float |
float |
Float64Array |
5.0x10-324 to 1.8x10308 | 8 | 64-bit IEEE floating point number (16 significant digits e.g. 1.123...15) | unrestricted double |
double |
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
方法
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
Specification | Status | Comment |
---|---|---|
Typed Array Specification | Obsolete | Defined as TypedArray and ArrayBufferView interface with typed array view types. Superseded by ECMAScript 6. |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'TypedArray Objects' in that specification. |
Standard | Initial definition in an ECMA standard. Specified behaviour for indexed and named properties. Specified that new is required. |
ECMAScript (ECMA-262) The definition of 'TypedArray Objects' in that specification. |
Living Standard |
瀏覽器相容性
BCD tables only load in the browser
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]);