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<pre class="metadata">
title: ArrayBuffer transfer
status: proposal
stage: 4
contributors: Shu-yu Guo, Jordan Harband, Yagiz Nizipli
location: https://github.com/tc39/proposal-arraybuffer-transfer
copyright: false
markEffects: true
</pre>

<emu-clause id="sec-new-abstract-operations-for-arraybuffer-objects" number="25.1.2">
  <h1>Abstract Operations for ArrayBuffer Objects</h1>

  <emu-clause id="sec-arraybuffercopyanddetach" type="abstract operation" number="14">
    <h1>
      <ins>
      ArrayBufferCopyAndDetach (
        _arrayBuffer_: an ECMAScript language value,
        _newLength_: an ECMAScript language value,
        _preserveResizability_: ~preserve-resizability~ or ~fixed-length~,
      ): either a normal completion containing an ArrayBuffer or a throw completion
      </ins>
    </h1>
    <dl class="header">
    </dl>
    <ins>
      <emu-alg>
        1. Perform ? RequireInternalSlot(_arrayBuffer_, [[ArrayBufferData]]).
        1. If IsSharedArrayBuffer(_arrayBuffer_) is *true*, throw a *TypeError* exception.
        1. If _newLength_ is *undefined*, then
          1. Let _newByteLength_ be _arrayBuffer_.[[ArrayBufferByteLength]].
        1. Else,
          1. Let _newByteLength_ be ? ToIndex(_newLength_).
        1. If IsDetachedBuffer(_arrayBuffer_) is *true*, throw a *TypeError* exception.
        1. If _preserveResizability_ is ~preserve-resizability~ and IsResizableArrayBuffer(_arrayBuffer_) is *true*, then
          1. Let _newMaxByteLength_ be _arrayBuffer_.[[ArrayBufferMaxByteLength]].
        1. Else,
          1. Let _newMaxByteLength_ be ~empty~.
        1. If _arrayBuffer_.[[ArrayBufferDetachKey]] is not *undefined*, throw a *TypeError* exception.
        1. Let _newBuffer_ be ? <emu-meta suppress-effects="user-code">AllocateArrayBuffer(%ArrayBuffer%, _newByteLength_, _newMaxByteLength_)</emu-meta>.
        1. Let _copyLength_ be min(_newByteLength_, _arrayBuffer_.[[ArrayBufferByteLength]]).
        1. Let _fromBlock_ be _arrayBuffer_.[[ArrayBufferData]].
        1. Let _toBlock_ be _newBuffer_.[[ArrayBufferData]].
        1. Perform CopyDataBlockBytes(_toBlock_, 0, _fromBlock_, 0, _copyLength_).
        1. NOTE: Neither creation of the new Data Block nor copying from the old Data Block are observable. Implementations may implement this method as a zero-copy move or a `realloc`.
        1. Perform ! DetachArrayBuffer(_arrayBuffer_).
        1. Return _newBuffer_.
      </emu-alg>
    </ins>
  </emu-clause>
</emu-clause>

<emu-clause id="sec-new-properties-of-the-arraybuffer-prototype-object" number="25.1.5">
  <h1>Properties of the ArrayBuffer Prototype Object</h1>

  <emu-clause id="sec-get-arraybuffer.prototype.detached" number="4">
    <h1>get ArrayBuffer.prototype.detached</h1>
    <p>`ArrayBuffer.prototype.detached` is an accessor property whose set accessor function is *undefined*. Its get accessor function performs the following steps:</p>
    <emu-alg>
      1. Let _O_ be the *this* value.
      1. Perform ? RequireInternalSlot(_O_, [[ArrayBufferData]]).
      1. If IsSharedArrayBuffer(_O_) is *true*, throw a *TypeError* exception.
      1. Return IsDetachedBuffer(_O_).
    </emu-alg>
  </emu-clause>

  <emu-clause id="sec-arraybuffer.prototype.transfer" number="5">
    <h1>ArrayBuffer.prototype.transfer ( [ _newLength_ ] )</h1>
    <p>This method performs the following steps when called:</p>
    <emu-alg>
      1. Let _O_ be the *this* value.
      1. Return ? ArrayBufferCopyAndDetach(_O_, _newLength_, ~preserve-resizability~).
    </emu-alg>
  </emu-clause>

  <emu-clause id="sec-arraybuffer.prototype.transfertofixedlength" number="6">
    <h1>ArrayBuffer.prototype.transferToFixedLength ( [ _newLength_ ] )</h1>
    <p>This method performs the following steps when called:</p>
    <emu-alg>
      1. Let _O_ be the *this* value.
      1. Return ? ArrayBufferCopyAndDetach(_O_, _newLength_, ~fixed-length~).
    </emu-alg>
  </emu-clause>
</emu-clause>