TypedArray
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
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.
Try it
Description
The TypedArray
constructor (often referred to as %TypedArray%
to indicate its "intrinsicness", since it does not correspond to any global exposed to a JavaScript program) serves as the common superclass of all TypedArray
subclasses. Think about %TypedArray%
as an "abstract class" providing a common interface of utility methods for all typed array subclasses. This constructor is not directly exposed: there is no global TypedArray
property. It is only accessible through Object.getPrototypeOf(Int8Array)
and similar.
When creating an instance of a TypedArray
subclass (e.g. Int8Array
), an array buffer is created internally in memory or, if an ArrayBuffer
object is given as constructor argument, that ArrayBuffer
is used instead. The buffer address is saved as an internal property of the instance and all the methods of %TypedArray%.prototype
will set and get values based on that array buffer address.
TypedArray objects
Type | Value Range | Size in bytes | Web IDL type |
---|---|---|---|
Int8Array |
-128 to 127 | 1 | byte |
Uint8Array |
0 to 255 | 1 | octet |
Uint8ClampedArray |
0 to 255 | 1 | octet |
Int16Array |
-32768 to 32767 | 2 | short |
Uint16Array |
0 to 65535 | 2 | unsigned short |
Int32Array |
-2147483648 to 2147483647 | 4 | long |
Uint32Array |
0 to 4294967295 | 4 | unsigned long |
Float16Array |
-65504 to 65504 |
2 | N/A |
Float32Array |
-3.4e38 to 3.4e38 |
4 | unrestricted float |
Float64Array |
-1.8e308 to 1.8e308 |
8 | unrestricted double |
BigInt64Array |
-263 to 263 - 1 | 8 | bigint |
BigUint64Array |
0 to 264 - 1 | 8 | bigint |
Value encoding and normalization
All typed arrays operate on ArrayBuffer
s, where you can observe the exact byte representation of each element, so how the numbers are encoded in binary format is significant.
- Unsigned integer arrays (
Uint8Array
,Uint16Array
,Uint32Array
, andBigUint64Array
) store the number directly in binary. - Signed integer arrays (
Int8Array
,Int16Array
,Int32Array
, andBigInt64Array
) store the number using two's complement. - Floating-point arrays (
Float16Array
,Float32Array
, andFloat64Array
) store the number using IEEE 754 floating-point format. TheNumber
reference has more information about the exact format. JavaScript numbers use double precision floating point format by default, which is the same asFloat64Array
.Float32Array
uses 23 (instead of 52) bits for the mantissa and 8 (instead of 11) bits for the exponent.Float16Array
uses 10 bits for the mantissa and 5 bits for the exponent. Note that the spec requires allNaN
values to use the same bit encoding, but the exact bit pattern is implementation-dependent. Uint8ClampedArray
is a special case. It stores the number in binary likeUint8Array
does, but when you store a number outside the range, it clamps the number to the range 0 to 255 by mathematical value, instead of truncating the most significant bits.
All typed arrays except Int8Array
, Uint8Array
, and Uint8ClampedArray
store each element using multiple bytes. These bytes can either be ordered from most significant to least significant (big-endian) or from least significant to most significant (little-endian). See Endianness for more explanation. Typed arrays always use the platform's native byte order. If you want to specify the endianness when writing and reading from buffers, you should use a DataView
instead.
When writing to these typed arrays, values that are outside the representable range are normalized.
- All integer arrays (except
Uint8ClampedArray
) use fixed-width number conversion, which first truncates the decimal part of the number and then takes the lowest bits. Uint8ClampedArray
first clamps the number to the range 0 to 255 (values greater than 255 become 255 and values less than 0 become 0). It then rounds (instead of flooring) the result to the nearest integer, with half-to-even; meaning if the number is exactly between two integers, it rounds to the nearest even integer. For example,0.5
becomes0
,1.5
becomes2
, and2.5
becomes2
.Float16Array
andFloat32Array
perform a "round to even" to convert 64-bit floating point numbers to 32-bit and 16-bit. This is the same algorithm as provided byMath.fround()
andMath.f16round()
.
Behavior when viewing a resizable buffer
When a TypedArray
is created as a view of a resizable buffer, resizing the underlying buffer will have different effects on the size of the TypedArray
depending on whether the TypedArray
is constructed as length-tracking.
If a typed array is created without a specific size by omitting the third parameter or passing undefined
, the typed array will become length-tracking, and will automatically resize to fit the underlying buffer
as the latter is resized:
const buffer = new ArrayBuffer(8, { maxByteLength: 16 });
const float32 = new Float32Array(buffer);
console.log(float32.byteLength); // 8
console.log(float32.length); // 2
buffer.resize(12);
console.log(float32.byteLength); // 12
console.log(float32.length); // 3
If a typed array is created with a specific size using the third length
parameter, it won't resize to contain the buffer
as the latter is grown:
const buffer = new ArrayBuffer(8, { maxByteLength: 16 });
const float32 = new Float32Array(buffer, 0, 2);
console.log(float32.byteLength); // 8
console.log(float32.length); // 2
console.log(float32[0]); // 0, the initial value
buffer.resize(12);
console.log(float32.byteLength); // 8
console.log(float32.length); // 2
console.log(float32[0]); // 0, the initial value
When a buffer
is shrunk, the viewing typed array may become out of bounds, in which case the typed array's observed size will decrease to 0. This is the only case where a non-length-tracking typed array's length may change.
const buffer = new ArrayBuffer(8, { maxByteLength: 16 });
const float32 = new Float32Array(buffer, 0, 2);
buffer.resize(7);
console.log(float32.byteLength); // 0
console.log(float32.length); // 0
console.log(float32[0]); // undefined
If you then grow the buffer
again to bring the typed array back in bounds, the typed array's size will be restored to its original value.
buffer.resize(8);
console.log(float32.byteLength); // 8
console.log(float32.length); // 2
console.log(float32[0]); // 0 - back in bounds again!
The same can happen for length-tracking typed arrays as well, if the buffer is shrunk beyond the byteOffset
.
const buffer = new ArrayBuffer(8, { maxByteLength: 16 });
const float32 = new Float32Array(buffer, 4);
// float32 is length-tracking, but it only extends from the 4th byte
// to the end of the buffer, so if the buffer is resized to be shorter
// than 4 bytes, the typed array will become out of bounds
buffer.resize(3);
console.log(float32.byteLength); // 0
Constructor
This object cannot be instantiated directly — attempting to construct it with new
throws a TypeError
.
new (Object.getPrototypeOf(Int8Array))();
// TypeError: Abstract class TypedArray not directly constructable
Instead, you create an instance of a typed array of a particular type, such as an 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
typedArray
-
When called with an instance of a
TypedArray
subclass, thetypedArray
gets copied into a new typed array. For a non-bigintTypedArray
constructor, thetypedArray
parameter can only be of one of the non-bigint types (such asInt32Array
). Similarly, for a bigintTypedArray
constructor (BigInt64Array
orBigUint64Array
), thetypedArray
parameter can only be of one of the bigint types. Each value intypedArray
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 thetypedArray
argument. object
-
When called with an object that's not a
TypedArray
instance, a new typed array is created in the same way as theTypedArray.from()
method. length
Optional-
When called with a non-object, the parameter will be treated as a number specifying the length of the typed array. An internal array buffer is created in memory, of size
length
multiplied byBYTES_PER_ELEMENT
bytes, filled with zeros. Omitting all parameters is equivalent to using0
aslength
. buffer
,byteOffset
Optional,length
Optional-
When called with an
ArrayBuffer
orSharedArrayBuffer
instance, and optionally abyteOffset
and alength
argument, a new typed array view is created that views the specified buffer. ThebyteOffset
(in bytes) andlength
(in number of elements, each occupyingBYTES_PER_ELEMENT
bytes) 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
starting frombyteOffset
is viewed. Iflength
is omitted, the typed array becomes length-tracking.
Exceptions
All TypeArray
subclass constructors operate in the same way. They would all throw the following exceptions:
TypeError
-
Thrown in one of the following cases:
- A
typedArray
is passed but it is a bigint type while the current constructor is not, or vice versa. - A
typedArray
is passed but the buffer it's viewing is detached, or a detachedbuffer
is directly passed.
- A
RangeError
-
Thrown in one of the following cases:
- The new typed array's length is too large.
- The length of
buffer
(if thelength
parameter is not specified) orbyteOffset
is not an integral multiple of the new typed array's element size. byteOffset
is not a valid array index (an integer between 0 and 253 - 1).- When creating a view from a buffer, the bounds are outside the buffer. In other words,
byteOffset + length * TypedArray.BYTES_PER_ELEMENT > buffer.byteLength
.
Static properties
These properties are defined on the TypedArray
constructor object and are thus shared by all TypedArray
subclass constructors.
TypedArray[Symbol.species]
-
The constructor function used to create derived objects.
All TypedArray
subclasses also have the following static properties:
TypedArray.BYTES_PER_ELEMENT
-
Returns a number value of the element size for the different
TypedArray
objects.
Static methods
These methods are defined on the TypedArray
constructor object and are thus shared by all TypedArray
subclass constructors.
TypedArray.from()
-
Creates a new
TypedArray
from an array-like or iterable object. See alsoArray.from()
. TypedArray.of()
-
Creates a new
TypedArray
with a variable number of arguments. See alsoArray.of()
.
Instance properties
These properties are defined on TypedArray.prototype
and shared by all TypedArray
subclass instances.
TypedArray.prototype.buffer
-
Returns the
ArrayBuffer
referenced by the typed array. TypedArray.prototype.byteLength
-
Returns the length (in bytes) of the typed array.
TypedArray.prototype.byteOffset
-
Returns the offset (in bytes) of the typed array from the start of its
ArrayBuffer
. TypedArray.prototype.constructor
-
The constructor function that created the instance object.
TypedArray.prototype.constructor
is the hiddenTypedArray
constructor function, but each typed array subclass also defines its ownconstructor
property. TypedArray.prototype.length
-
Returns the number of elements held in the typed array.
TypedArray.prototype[Symbol.toStringTag]
-
The initial value of the
TypedArray.prototype[Symbol.toStringTag]
property is a getter that returns the same string as the typed array constructor's name. It returnsundefined
if thethis
value is not one of the typed array subclasses. This property is used inObject.prototype.toString()
. However, becauseTypedArray
also has its owntoString()
method, this property is not used unless you callObject.prototype.toString.call()
with a typed array asthisArg
.
All TypedArray
subclasses also have the following instance properties:
TypedArray.prototype.BYTES_PER_ELEMENT
-
Returns a number value of the element size for the different
TypedArray
objects.
Instance methods
These methods are defined on the TypedArray
prototype object and are thus shared by all TypedArray
subclass instances.
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 alsoArray.prototype.filter()
. TypedArray.prototype.find()
-
Returns the first
element
in the array that satisfies a provided testing function, orundefined
if no appropriate element is found. See alsoArray.prototype.find()
. TypedArray.prototype.findIndex()
-
Returns the first index value in the array that has an element that satisfies a provided testing function, or
-1
if no appropriate element was found. See alsoArray.prototype.findIndex()
. TypedArray.prototype.findLast()
-
Returns the value of the last element in the array that satisfies a provided testing function, or
undefined
if no appropriate element is found. See alsoArray.prototype.findLast()
. TypedArray.prototype.findLastIndex()
-
Returns the index of the last element in the array that satisfies a provided testing function, or
-1
if no appropriate element was found. See alsoArray.prototype.findLastIndex()
. 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
orfalse
as appropriate. See alsoArray.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 alsoArray.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 alsoArray.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 alsoArray.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.toLocaleString()
-
Returns a localized string representing the array and its elements. See also
Array.prototype.toLocaleString()
. TypedArray.prototype.toReversed()
-
Returns a new array with the elements in reversed order, without modifying the original array.
TypedArray.prototype.toSorted()
-
Returns a new array with the elements sorted in ascending order, without modifying the original array.
TypedArray.prototype.toString()
-
Returns a string representing the array and its elements. See also
Array.prototype.toString()
. 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.with()
-
Returns a new array with the element at the given index replaced with the given value, without modifying the original array.
TypedArray.prototype[Symbol.iterator]()
-
Returns a new array iterator object that contains the values for each index in the array.
Examples
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
const 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
TypedArray
s 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
Specification |
---|
ECMAScript Language Specification # sec-typedarray-objects |
Browser compatibility
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