DataView - JavaScript 编辑

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.

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 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

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

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

Specifications

Browser compatibility

BCD tables only load in the browser

See also

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