DataView

The DataView view provides a low-level interface for reading and writing multiple number types in a binary ArrayBuffer, without having to care about the platform's endianness.

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.

Syntax

new DataView(buffer [, byteOffset [, byteLength]])

Parameters

buffer

An existing ArrayBuffer or SharedArrayBuffer to use as the storage backing the new DataView object.

byteOffset Optional

The offset, in bytes, to the first byte in the above buffer for the new view to reference. If unspecified, the buffer view starts with the first byte.

byteLength Optional

The number of elements in the byte array. If unspecified, the view's length will match the buffer's length.

Return value

A new DataView object representing the specified data buffer. (That probably wasn't a very helpful description.)

You can think of the returned object as an "interpreter" of the array buffer of bytes — it knows how to convert numbers to fit within the buffer correctly, both when reading and writing to it. This means handling integer and float conversion, endianness, and other details of representing numbers in binary form.

Exceptions

RangeError

Thrown if the byteOffset or byteLength parameter values result in the view extending past the end of the buffer.

For example, if the buffer is 16 bytes long, the byteOffset is 8, and the byteLength is 10, this error is thrown because the resulting view tries to extend 2 bytes past the total length of the buffer.

Description

Endianness

Multi-byte number formats are represented in memory differently depending on machine architecture — see Endianness for an explanation. DataView accessors provide explicit control of how data is accessed, regardless of the executing computer's endianness.

var littleEndian = (function() {
  var buffer = new ArrayBuffer(2);
  new DataView(buffer).setInt16(0, 256, true /* littleEndian */);
  // Int16Array uses the platform's endianness.
  return new Int16Array(buffer)[0] === 256;
})();
console.log(littleEndian); // true or false

64-bit Integer Values

Because JavaScript does not currently include standard support for 64-bit integer values, DataView does not offer native 64-bit operations.  As a workaround, you could implement your own getUint64() function to obtain a value with precision up to Number.MAX_SAFE_INTEGER, which could suffice for certain cases.

function getUint64(dataview, byteOffset, littleEndian) {
  // split 64-bit number into two 32-bit (4-byte) parts
  const left =  dataview.getUint32(byteOffset, littleEndian);
  const right = dataview.getUint32(byteOffset+4, littleEndian);

  // combine the two 32-bit values
  const combined = littleEndian? left + 2**32*right : 2**32*left + right;

  if (!Number.isSafeInteger(combined))
    console.warn(combined, 'exceeds MAX_SAFE_INTEGER. Precision may be lost');

  return combined;
}

Alternatively, if you need full 64-bit range, you can create a BigInt. Further, although native BigInts are much faster than user-land library equivelents, BigInts will always be much slower than 32-bit integers in JavaScript due to the nature of their variable size.

const BigInt = window.BigInt, bigThirtyTwo = BigInt(32), bigZero = BigInt(0);
function getUint64BigInt(dataview, byteOffset, littleEndian) {
  // split 64-bit number into two 32-bit (4-byte) parts
  const left = BigInt(dataview.getUint32(byteOffset|0, !!littleEndian)>>>0);
  const right = BigInt(dataview.getUint32((byteOffset|0) + 4|0, !!littleEndian)>>>0);

  // combine the two 32-bit values and return
  return littleEndian ? (right<<bigThirtyTwo)|left : (left<<bigThirtyTwo)|right;
}

Properties

All DataView instances inherit from DataView.prototype and allows the addition of properties to all DataView objects.

DataView.prototype.constructor

Specifies the function that creates an object's prototype. The initial value is the standard built-in DataView constructor.

DataView.prototype.buffer Read only

The ArrayBuffer referenced by this view. Fixed at construction time and thus read only.

DataView.prototype.byteLength Read only

The length (in bytes) of this view from the start of its ArrayBuffer. Fixed at construction time and thus read only.

DataView.prototype.byteOffset Read only

The offset (in bytes) of this view from the start of its ArrayBuffer. Fixed at construction time and thus read only.

Methods

Read

DataView.prototype.getInt8()

Gets a signed 8-bit integer (byte) at the specified byte offset from the start of the view.

DataView.prototype.getUint8()

Gets an unsigned 8-bit integer (unsigned byte) at the specified byte offset from the start of the view.

DataView.prototype.getInt16()

Gets a signed 16-bit integer (short) at the specified byte offset from the start of the view.

DataView.prototype.getUint16()

Gets an unsigned 16-bit integer (unsigned short) at the specified byte offset from the start of the view.

DataView.prototype.getInt32()

Gets a signed 32-bit integer (long) at the specified byte offset from the start of the view.

DataView.prototype.getUint32()

Gets an unsigned 32-bit integer (unsigned long) at the specified byte offset from the start of the view.

DataView.prototype.getFloat32()

Gets a signed 32-bit float (float) at the specified byte offset from the start of the view.

DataView.prototype.getFloat64()

Gets a signed 64-bit float (double) at the specified byte offset from the start of the view.

DataView.prototype.getBigInt64()

Gets a signed 64-bit integer (long long) at the specified byte offset from the start of the view.

DataView.prototype.getBigUint64()

Gets an unsigned 64-bit integer (unsigned long long) at the specified byte offset from the start of the view.

Write

DataView.prototype.setInt8()

Stores a signed 8-bit integer (byte) value at the specified byte offset from the start of the view.

DataView.prototype.setUint8()

Stores an unsigned 8-bit integer (unsigned byte) value at the specified byte offset from the start of the view.

DataView.prototype.setInt16()

Stores a signed 16-bit integer (short) value at the specified byte offset from the start of the view.

DataView.prototype.setUint16()

Stores an unsigned 16-bit integer (unsigned short) value at the specified byte offset from the start of the view.

DataView.prototype.setInt32()

Stores a signed 32-bit integer (long) value at the specified byte offset from the start of the view.

DataView.prototype.setUint32()

Stores an unsigned 32-bit integer (unsigned long) value at the specified byte offset from the start of the view.

DataView.prototype.setFloat32()

Stores a signed 32-bit float (float) value at the specified byte offset from the start of the view.

DataView.prototype.setFloat64()

Stores a signed 64-bit float (double) value at the specified byte offset from the start of the view.

DataView.prototype.setBigInt64()

Stores a signed 64-bit integer (long long) value at the specified byte offset from the start of the view.

DataView.prototype.setBigUint64()

Stores an unsigned 64-bit integer (unsigned long long) value at the specified byte offset from the start of the view.

Example

var buffer = new ArrayBuffer(16);
var view = new DataView(buffer, 0);

view.setInt16(1, 42);
view.getInt16(1); // 42

Specifications

Browser compatibility

Compatibility notes

Starting with Firefox 40, DataView must be constructed with the new operator. Calling DataView() as a function without new will throw a TypeError.

var view = DataView(buffer, 0); 
// TypeError: calling a builtin DataView constructor without new is forbidden

var view = new DataView(buffer, 0);

See also

• jDataView: JavaScript library that polyfills and extends the DataView API to all browsers and Node.js.
• ArrayBuffer
• SharedArrayBuffer