ECMAScript® 2021 Language Specification

Draft ECMA-262 / March 3, 2021

25.3 DataView Objects

25.3.1 Abstract Operations For DataView Objects

25.3.1.1 GetViewValue ( view, requestIndex, isLittleEndian, type )

The abstract operation GetViewValue takes arguments view, requestIndex, isLittleEndian, and type. It is used by functions on DataView instances to retrieve values from the view's buffer. It performs the following steps when called:

  1. Perform ? RequireInternalSlot(view, [[DataView]]).
  2. Assert: view has a [[ViewedArrayBuffer]] internal slot.
  3. Let getIndex be ? ToIndex(requestIndex).
  4. Set isLittleEndian to ! ToBoolean(isLittleEndian).
  5. Let buffer be view.[[ViewedArrayBuffer]].
  6. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
  7. Let viewOffset be view.[[ByteOffset]].
  8. Let viewSize be view.[[ByteLength]].
  9. Let elementSize be the Element Size value specified in Table 60 for Element Type type.
  10. If getIndex + elementSize > viewSize, throw a RangeError exception.
  11. Let bufferIndex be getIndex + viewOffset.
  12. Return GetValueFromBuffer(buffer, bufferIndex, type, false, Unordered, isLittleEndian).

25.3.1.2 SetViewValue ( view, requestIndex, isLittleEndian, type, value )

The abstract operation SetViewValue takes arguments view, requestIndex, isLittleEndian, type, and value. It is used by functions on DataView instances to store values into the view's buffer. It performs the following steps when called:

  1. Perform ? RequireInternalSlot(view, [[DataView]]).
  2. Assert: view has a [[ViewedArrayBuffer]] internal slot.
  3. Let getIndex be ? ToIndex(requestIndex).
  4. If ! IsBigIntElementType(type) is true, let numberValue be ? ToBigInt(value).
  5. Otherwise, let numberValue be ? ToNumber(value).
  6. Set isLittleEndian to ! ToBoolean(isLittleEndian).
  7. Let buffer be view.[[ViewedArrayBuffer]].
  8. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
  9. Let viewOffset be view.[[ByteOffset]].
  10. Let viewSize be view.[[ByteLength]].
  11. Let elementSize be the Element Size value specified in Table 60 for Element Type type.
  12. If getIndex + elementSize > viewSize, throw a RangeError exception.
  13. Let bufferIndex be getIndex + viewOffset.
  14. Return SetValueInBuffer(buffer, bufferIndex, type, numberValue, false, Unordered, isLittleEndian).

25.3.2 The DataView Constructor

The DataView constructor:

  • is %DataView%.
  • is the initial value of the "DataView" property of the global object.
  • creates and initializes a new DataView object when called as a constructor.
  • is not intended to be called as a function and will throw an exception when called in that manner.
  • is designed to be subclassable. It may be used as the value of an extends clause of a class definition. Subclass constructors that intend to inherit the specified DataView behaviour must include a super call to the DataView constructor to create and initialize subclass instances with the internal state necessary to support the DataView.prototype built-in methods.

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

When the DataView function is called with at least one argument buffer, the following steps are taken:

  1. If NewTarget is undefined, throw a TypeError exception.
  2. Perform ? RequireInternalSlot(buffer, [[ArrayBufferData]]).
  3. Let offset be ? ToIndex(byteOffset).
  4. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
  5. Let bufferByteLength be buffer.[[ArrayBufferByteLength]].
  6. If offset > bufferByteLength, throw a RangeError exception.
  7. If byteLength is undefined, then
    1. Let viewByteLength be bufferByteLength - offset.
  8. Else,
    1. Let viewByteLength be ? ToIndex(byteLength).
    2. If offset + viewByteLength > bufferByteLength, throw a RangeError exception.
  9. Let O be ? OrdinaryCreateFromConstructor(NewTarget, "%DataView.prototype%", « [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], [[ByteOffset]] »).
  10. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
  11. Set O.[[ViewedArrayBuffer]] to buffer.
  12. Set O.[[ByteLength]] to viewByteLength.
  13. Set O.[[ByteOffset]] to offset.
  14. Return O.

25.3.3 Properties of the DataView Constructor

The DataView constructor:

  • has a [[Prototype]] internal slot whose value is %Function.prototype%.
  • has the following properties:

25.3.3.1 DataView.prototype

The initial value of DataView.prototype is the DataView prototype object.

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

25.3.4 Properties of the DataView Prototype Object

The DataView prototype object:

  • is %DataView.prototype%.
  • has a [[Prototype]] internal slot whose value is %Object.prototype%.
  • is an ordinary object.
  • does not have a [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], or [[ByteOffset]] internal slot.

25.3.4.1 get DataView.prototype.buffer

DataView.prototype.buffer is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

  1. Let O be the this value.
  2. Perform ? RequireInternalSlot(O, [[DataView]]).
  3. Assert: O has a [[ViewedArrayBuffer]] internal slot.
  4. Let buffer be O.[[ViewedArrayBuffer]].
  5. Return buffer.

25.3.4.2 get DataView.prototype.byteLength

DataView.prototype.byteLength is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

  1. Let O be the this value.
  2. Perform ? RequireInternalSlot(O, [[DataView]]).
  3. Assert: O has a [[ViewedArrayBuffer]] internal slot.
  4. Let buffer be O.[[ViewedArrayBuffer]].
  5. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
  6. Let size be O.[[ByteLength]].
  7. Return 𝔽(size).

25.3.4.3 get DataView.prototype.byteOffset

DataView.prototype.byteOffset is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

  1. Let O be the this value.
  2. Perform ? RequireInternalSlot(O, [[DataView]]).
  3. Assert: O has a [[ViewedArrayBuffer]] internal slot.
  4. Let buffer be O.[[ViewedArrayBuffer]].
  5. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
  6. Let offset be O.[[ByteOffset]].
  7. Return 𝔽(offset).

25.3.4.4 DataView.prototype.constructor

The initial value of DataView.prototype.constructor is %DataView%.

25.3.4.5 DataView.prototype.getBigInt64 ( byteOffset [ , littleEndian ] )

When the getBigInt64 method is called with argument byteOffset and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. Return ? GetViewValue(v, byteOffset, littleEndian, BigInt64).

25.3.4.6 DataView.prototype.getBigUint64 ( byteOffset [ , littleEndian ] )

When the getBigUint64 method is called with argument byteOffset and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. Return ? GetViewValue(v, byteOffset, littleEndian, BigUint64).

25.3.4.7 DataView.prototype.getFloat32 ( byteOffset [ , littleEndian ] )

When the getFloat32 method is called with argument byteOffset and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? GetViewValue(v, byteOffset, littleEndian, Float32).

25.3.4.8 DataView.prototype.getFloat64 ( byteOffset [ , littleEndian ] )

When the getFloat64 method is called with argument byteOffset and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? GetViewValue(v, byteOffset, littleEndian, Float64).

25.3.4.9 DataView.prototype.getInt8 ( byteOffset )

When the getInt8 method is called with argument byteOffset, the following steps are taken:

  1. Let v be the this value.
  2. Return ? GetViewValue(v, byteOffset, true, Int8).

25.3.4.10 DataView.prototype.getInt16 ( byteOffset [ , littleEndian ] )

When the getInt16 method is called with argument byteOffset and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? GetViewValue(v, byteOffset, littleEndian, Int16).

25.3.4.11 DataView.prototype.getInt32 ( byteOffset [ , littleEndian ] )

When the getInt32 method is called with argument byteOffset and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? GetViewValue(v, byteOffset, littleEndian, Int32).

25.3.4.12 DataView.prototype.getUint8 ( byteOffset )

When the getUint8 method is called with argument byteOffset, the following steps are taken:

  1. Let v be the this value.
  2. Return ? GetViewValue(v, byteOffset, true, Uint8).

25.3.4.13 DataView.prototype.getUint16 ( byteOffset [ , littleEndian ] )

When the getUint16 method is called with argument byteOffset and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? GetViewValue(v, byteOffset, littleEndian, Uint16).

25.3.4.14 DataView.prototype.getUint32 ( byteOffset [ , littleEndian ] )

When the getUint32 method is called with argument byteOffset and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? GetViewValue(v, byteOffset, littleEndian, Uint32).

25.3.4.15 DataView.prototype.setBigInt64 ( byteOffset, value [ , littleEndian ] )

When the setBigInt64 method is called with arguments byteOffset and value and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. Return ? SetViewValue(v, byteOffset, littleEndian, BigInt64, value).

25.3.4.16 DataView.prototype.setBigUint64 ( byteOffset, value [ , littleEndian ] )

When the setBigUint64 method is called with arguments byteOffset and value and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. Return ? SetViewValue(v, byteOffset, littleEndian, BigUint64, value).

25.3.4.17 DataView.prototype.setFloat32 ( byteOffset, value [ , littleEndian ] )

When the setFloat32 method is called with arguments byteOffset and value and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? SetViewValue(v, byteOffset, littleEndian, Float32, value).

25.3.4.18 DataView.prototype.setFloat64 ( byteOffset, value [ , littleEndian ] )

When the setFloat64 method is called with arguments byteOffset and value and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? SetViewValue(v, byteOffset, littleEndian, Float64, value).

25.3.4.19 DataView.prototype.setInt8 ( byteOffset, value )

When the setInt8 method is called with arguments byteOffset and value, the following steps are taken:

  1. Let v be the this value.
  2. Return ? SetViewValue(v, byteOffset, true, Int8, value).

25.3.4.20 DataView.prototype.setInt16 ( byteOffset, value [ , littleEndian ] )

When the setInt16 method is called with arguments byteOffset and value and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? SetViewValue(v, byteOffset, littleEndian, Int16, value).

25.3.4.21 DataView.prototype.setInt32 ( byteOffset, value [ , littleEndian ] )

When the setInt32 method is called with arguments byteOffset and value and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? SetViewValue(v, byteOffset, littleEndian, Int32, value).

25.3.4.22 DataView.prototype.setUint8 ( byteOffset, value )

When the setUint8 method is called with arguments byteOffset and value, the following steps are taken:

  1. Let v be the this value.
  2. Return ? SetViewValue(v, byteOffset, true, Uint8, value).

25.3.4.23 DataView.prototype.setUint16 ( byteOffset, value [ , littleEndian ] )

When the setUint16 method is called with arguments byteOffset and value and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? SetViewValue(v, byteOffset, littleEndian, Uint16, value).

25.3.4.24 DataView.prototype.setUint32 ( byteOffset, value [ , littleEndian ] )

When the setUint32 method is called with arguments byteOffset and value and optional argument littleEndian, the following steps are taken:

  1. Let v be the this value.
  2. If littleEndian is not present, set littleEndian to false.
  3. Return ? SetViewValue(v, byteOffset, littleEndian, Uint32, value).

25.3.4.25 DataView.prototype [ @@toStringTag ]

The initial value of the @@toStringTag property is the String value "DataView".

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

25.3.5 Properties of DataView Instances

DataView instances are ordinary objects that inherit properties from the DataView prototype object. DataView instances each have [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], and [[ByteOffset]] internal slots.

Note

The value of the [[DataView]] internal slot is not used within this specification. The simple presence of that internal slot is used within the specification to identify objects created using the DataView constructor.