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.

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.

const littleEndian = (function() {
  const 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

Some browsers don't have support for DataView.prototype.setBigInt64() and DataView.prototype.setBigUint64(). So to enable 64-bit operations in your code that will work across browsers, you could implement your own getUint64() function, to obtain values 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 equivalents, 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;
}

Constructor

DataView(): Creates a new DataView object.

Instance properties

DataView.prototype.buffer: The ArrayBuffer referenced by this view. Fixed at construction time and thus read only.
DataView.prototype.byteLength: The length (in bytes) of this view from the start of its ArrayBuffer. Fixed at construction time and thus read only.
DataView.prototype.byteOffset: The offset (in bytes) of this view from the start of its ArrayBuffer. Fixed at construction time and thus read only.

Instance methods

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.
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.

Examples

Using DataView

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

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

Specifications

Specification
ECMAScript Language Specification # sec-dataview-objects

Browser compatibility

BCD tables only load in the browser