TypedArray

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.

Description

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]].

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.

TypedArray objects

Constructor

This object cannot be instantiated directly. Instead, you create an instance of an array of a particular type, such as a Int8Array or a BigInt64Array. These objects all have a common syntax for their constructors:

new TypedArray()
new TypedArray(length)
new TypedArray(typedArray)
new TypedArray(object)

new TypedArray(buffer)
new TypedArray(buffer, byteOffset)
new TypedArray(buffer, byteOffset, length)

Where TypedArray is a constructor for one of the concrete types.

Parameters

length

When called with a length argument, an internal array buffer is created in memory, of size length multiplied by BYTES_PER_ELEMENT bytes, containing zeros.

typedArray

When called with a typedArray argument, the typedArray gets copied into a new typed array. For a non-bigint TypedArray, the typedArray parameter can be an object of only the non-bigint typed array types (such as Int32Array). Similarly, for a bigint TypedArray, the typedArray parameter can be an object of only the bigint typed array types (such as BigInt64Array). Each value in typedArray is converted to the corresponding type of the constructor before being copied into the new array. The length of the new typed array will be same as the length of the typedArray argument.

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.

Static properties

TypedArray.BYTES_PER_ELEMENT

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

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 for TypedArray objects.

Static methods

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().

Instance properties

TypedArray.prototype.buffer

Returns the ArrayBuffer referenced by the typed array. Fixed at construction time and thus read only.

TypedArray.prototype.byteLength

Returns the length (in bytes) of the typed array. Fixed at construction time and thus read only.

TypedArray.prototype.byteOffset

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

Returns the number of elements held in the typed array. Fixed at construction time and thus read only.

Instance methods

TypedArray.prototype.at()

Takes an integer value and returns the item at that index. This method allows for negative integers, which count back from the last item.

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.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.

Examples

New is required

Starting with ECMAScript 2015, TypedArray constructors must be constructed with the new operator. Calling a TypedArray constructor as a function without new will throw a TypeError.

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

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

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"

Cannot be frozen

TypedArrays that aren't empty cannot be frozen, as their underlying ArrayBuffer could be mutated through another TypedArray view of the buffer. This would mean that the object would never genuinely be frozen.

const i8 = Int8Array.of(1, 2, 3);
Object.freeze(i8);
// TypeError: Cannot freeze array buffer views with elements

ByteOffset must be aligned

When constructing a TypedArray as a view onto an ArrayBuffer, the byteOffset argument must be aligned to its element size; in other words, the offset must be a multiple of BYTES_PER_ELEMENT.

const i32 = new Int32Array(new ArrayBuffer(4), 1);
// RangeError: start offset of Int32Array should be a multiple of 4

const i32 = new Int32Array(new ArrayBuffer(4), 0);

ByteLength must be aligned

Like the byteOffset parameter, the byteLength property of an ArrayBuffer passed to a TypedArray's constructor must be a multiple of the constructor's BYTES_PER_ELEMENT.

const i32 = new Int32Array(new ArrayBuffer(3));
// RangeError: byte length of Int32Array should be a multiple of 4

const i32 = new Int32Array(new ArrayBuffer(4));

Specifications

Browser compatibility

See also

• A polyfill of typed arrays is available in core-js
• JavaScript typed arrays
• ArrayBuffer
• DataView
• TextDecoder — Helper that decode strings from numerical data