TypedArray

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Summary

A TypedArray object describes an array-like view of an underlying binary data buffer. There is no global property named TypedArray, nor is there a directly visible TypedArray constructor. Instead, there are a number of different global properties, whose values are typed array constructors for specific element types, listed below. On the following pages you will find common properties and methods that can be used with any typed array containing elements of any type.

Syntax

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();

Parameters

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 optional 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.

Description

ECMAScript 6 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.prototype) 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.

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 objects

Type Size Description Web IDL type Equivalent C type
Int8Array 1 8-bit twos complement signed integer byte int8_t
Uint8Array 1 8-bit unsigned integer octet uint8_t
Uint8ClampedArray 1 8-bit unsigned integer (clamped) octet uint8_t
Int16Array 2 16-bit twos complement signed integer short int16_t
Uint16Array 2 16-bit unsigned integer unsigned short uint16_t
Int32Array 4 32-bit twos complement signed integer long int32_t
Uint32Array 4 32-bit unsigned integer unsigned long uint32_t
Float32Array 4 32-bit IEEE floating point number unrestricted float float
Float64Array 8 64-bit IEEE floating point number unrestricted double double

Properties

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 3.
TypedArray.name
Returns the string value of the constructor name. E.g "Int8Array".
TypedArray.prototype
Prototype for the TypedArray objects.

Methods

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 prototype

All TypedArrays inherit from TypedArray.prototype.

Properties

TypedArray.prototype.constructor
Returns the function that created an instance's prototype. This is one the corresponding typed array type functions by default.
TypedArray.prototype.buffer Read only
Returns the ArrayBuffer referenced by the typed array. Fixed at construction time and thus read only.
TypedArray.prototype.byteLength Read only
Returns the length (in bytes) of the typed array from the start of its ArrayBuffer. Fixed at construction time and thus read only.
TypedArray.prototype.byteOffset Read only
Returns the offset (in bytes) of the typed array from the start of its ArrayBuffer. Fixed at construction time and thus read only.
TypedArray.prototype.length Read only
Returns the number of elements hold in the typed array. Fixed at construction time and thus read only.

Methods

TypedArray.prototype.copyWithin()
Copies a sequence of array elements within the array. See also Array.prototype.copyWithin().
TypedArray.prototype.entries()
Returns a new Array Iterator object that contains the key/value pairs for each index in the array. See also Array.prototype.entries().
TypedArray.prototype.every()
Tests whether all elements in the array pass the test provided by a function. See also Array.prototype.every().
TypedArray.prototype.fill()
Fills all the elements of an array from a start index to an end index with a static value. See also Array.prototype.fill().
TypedArray.prototype.filter()
Creates a new array with all of the elements of this array for which the provided filtering function returns true. See also Array.prototype.filter().
TypedArray.prototype.find()
Returns the found value in the array, if an element in the array satisfies the provided testing function or undefined if not found. See also Array.prototype.find().
TypedArray.prototype.findIndex()
Returns the found index in the array, if an element in the array satisfies the provided testing function or -1 if not found. See also Array.prototype.findIndex().
TypedArray.prototype.forEach()
Calls a function for each element in the array. See also Array.prototype.forEach().
TypedArray.prototype.includes()
Determines whether a typed array includes a certain element, returning true or false as appropriate. See also Array.prototype.includes().
TypedArray.prototype.indexOf()
Returns the first (least) index of an element within the array equal to the specified value, or -1 if none is found. See also Array.prototype.indexOf().
TypedArray.prototype.join()
Joins all elements of an array into a string. See also Array.prototype.join().
TypedArray.prototype.keys()
Returns a new Array Iterator that contains the keys for each index in the array. See also Array.prototype.keys().
TypedArray.prototype.lastIndexOf()
Returns the last (greatest) index of an element within the array equal to the specified value, or -1 if none is found. See also Array.prototype.lastIndexOf().
TypedArray.prototype.map()
Creates a new array with the results of calling a provided function on every element in this array. See also Array.prototype.map().
TypedArray.prototype.move() Unimplemented
Former non-standard version of TypedArray.prototype.copyWithin().
TypedArray.prototype.reduce()
Apply a function against an accumulator and each value of the array (from left-to-right) as to reduce it to a single value. See also Array.prototype.reduce().
TypedArray.prototype.reduceRight()
Apply a function against an accumulator and each value of the array (from right-to-left) as to reduce it to a single value. See also Array.prototype.reduceRight().
TypedArray.prototype.reverse()
Reverses the order of the elements of an array — the first becomes the last, and the last becomes the first. See also Array.prototype.reverse().
TypedArray.prototype.set()
Stores multiple values in the typed array, reading input values from a specified array.
TypedArray.prototype.slice()
Extracts a section of an array and returns a new array. See also Array.prototype.slice().
TypedArray.prototype.some()
Returns true if at least one element in this array satisfies the provided testing function. See also Array.prototype.some().
TypedArray.prototype.sort()
Sorts the elements of an array in place and returns the array. See also Array.prototype.sort().
TypedArray.prototype.subarray()
Returns a new TypedArray from the given start and end element index.
TypedArray.prototype.values()
Returns a new Array Iterator object that contains the values for each index in the array. See also Array.prototype.values().
TypedArray.prototype.toLocaleString()
Returns a localized string representing the array and its elements. See also Array.prototype.toLocaleString().
TypedArray.prototype.toString()
Returns a string representing the array and its elements. See also Array.prototype.toString().
TypedArray.prototype[@@iterator]()
Returns a new Array Iterator object that contains the values for each index in the array.

Specifications

Specification Status Comment
Typed Array Specification Obsolete Defined as TypedArray and ArrayBufferView interface with typed array view types. Superseded by ECMAScript 6.
ECMAScript 6 (ECMA-262)
The definition of 'TypedArray Objects' in that specification.
勧告候補 Initial definition in an ECMA standard.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 7.0 4.0 (2) 10 11.6 5.1
Indexed properties not consulting prototype (Yes) (see [1]) 25 (25) ? ? ?
Named properties (Yes) 30 (30) ? ? ?
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support 4.0 (Yes) 4.0 (2) 10 11.6 4.2
Indexed properties not consulting prototype ? (Yes) (see [1]) 25.0 (25) ? ? ?
Named properties ? (Yes) 30.0 (30) ? ? ?

Notes
[1] -1 and similar are not considered as indexed properties and therefore return the value of the prototype property.

See also

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Contributors to this page: teoli, ethertank, yyss
最終更新者: teoli,
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