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 = (() => {
  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

These properties are defined on DataView.prototype and shared by all DataView instances.

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. 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.
DataView.prototype.constructor: The constructor function that created the instance object. For DataView instances, the initial value is the DataView constructor.
DataView.prototype[@@toStringTag]: The initial value of the @@toStringTag property is the string "DataView". This property is used in Object.prototype.toString().

Instance methods

DataView.prototype.getBigInt64(): Reads 8 bytes starting at the specified byte offset of this DataView and interprets them as a 64-bit signed integer.
DataView.prototype.getBigUint64(): Reads 8 bytes starting at the specified byte offset of this DataView and interprets them as a 64-bit unsigned integer.
DataView.prototype.getFloat32(): Reads 4 bytes starting at the specified byte offset of this DataView and interprets them as a 32-bit floating point number.
DataView.prototype.getFloat64(): Reads 8 bytes starting at the specified byte offset of this DataView and interprets them as a 64-bit floating point number.
DataView.prototype.getInt16(): Reads 2 bytes starting at the specified byte offset of this DataView and interprets them as a 16-bit signed integer.
DataView.prototype.getInt32(): Reads 4 bytes starting at the specified byte offset of this DataView and interprets them as a 32-bit signed integer.
DataView.prototype.getInt8(): Reads 1 byte at the specified byte offset of this DataView and interprets it as an 8-bit signed integer.
DataView.prototype.getUint16(): Reads 2 bytes starting at the specified byte offset of this DataView and interprets them as a 16-bit unsigned integer.
DataView.prototype.getUint32(): Reads 4 bytes starting at the specified byte offset of this DataView and interprets them as a 32-bit unsigned integer.
DataView.prototype.getUint8(): Reads 1 byte at the specified byte offset of this DataView and interprets it as an 8-bit unsigned integer.
DataView.prototype.setBigInt64(): Takes a BigInt and stores it as a 64-bit signed integer in the 8 bytes starting at the specified byte offset of this DataView.
DataView.prototype.setBigUint64(): Takes a BigInt and stores it as a 64-bit unsigned integer in the 8 bytes starting at the specified byte offset of this DataView.
DataView.prototype.setFloat32(): Takes a number and stores it as a 32-bit float in the 4 bytes starting at the specified byte offset of this DataView.
DataView.prototype.setFloat64(): Takes a number and stores it as a 64-bit float in the 8 bytes starting at the specified byte offset of this DataView.
DataView.prototype.setInt16(): Takes a number and stores it as a 16-bit signed integer in the 2 bytes at the specified byte offset of this DataView.
DataView.prototype.setInt32(): Takes a number and stores it as a 32-bit signed integer in the 4 bytes at the specified byte offset of this DataView.
DataView.prototype.setInt8(): Takes a number and stores it as an 8-bit signed integer in the byte at the specified byte offset of this DataView.
DataView.prototype.setUint16(): Takes a number and stores it as a 16-bit unsigned integer in the 2 bytes at the specified byte offset of this DataView.
DataView.prototype.setUint32(): Takes a number and stores it as a 32-bit unsigned integer in the 4 bytes at the specified byte offset of this DataView.
DataView.prototype.setUint8(): Takes a number and stores it as an 8-bit unsigned integer in the byte at the specified byte offset of this DataView.

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