proposal-typedarray-concat/spec.emu at 7672833bc4383873adc967a81e59b67273b81364 · tc39/proposal-typedarray-concat · GitHub

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<pre class="metadata">
title: TypedArray.concat
stage: 1
contributors: James M Snell
</pre>

<emu-clause id="sec-typedarray-objects">
  <h1>TypedArray Objects</h1>

  <emu-clause id="sec-%typedarray%-intrinsic-object">
    <h1>The %TypedArray% Intrinsic Object</h1>

    <emu-clause id="sec-properties-of-the-%typedarray%-intrinsic-object">
      <h1>Properties of the %TypedArray% Intrinsic Object</h1>

      <emu-clause id="sec-%typedarray%.concat">
        <h1>%TypedArray%.concat ( _items_ [ , _length_ ] )</h1>
        <p>This method concatenates the elements of multiple TypedArrays of the same type into a new TypedArray. It performs the following steps when called:</p>
        <emu-alg>
          1. Let _C_ be the *this* value.
          1. If IsConstructor(_C_) is *false*, throw a *TypeError* exception.
          1. If _C_ does not have a [[TypedArrayName]] internal slot, throw a *TypeError* exception.
          1. Let _arrayList_ be ? IteratorToList(? GetIteratorFromMethod(_items_, ? GetMethod(_items_, %Symbol.iterator%))).
          1. Let _totalLength_ be 0.
          1. Let _elementType_ be TypedArrayElementType(_C_).
          1. For each element _item_ of _arrayList_, do
            1. Let _taRecord_ be ? ValidateTypedArray(_item_, ~seq-cst~).
            1. If TypedArrayElementType(_item_) is not _elementType_, throw a *TypeError* exception.
            1. Let _itemLength_ be TypedArrayLength(_taRecord_).
            1. Set _totalLength_ to _totalLength_ + _itemLength_.
          1. If _length_ is present and _length_ is not *undefined*, then
            1. Let _newLength_ be ? ToIndex(_length_).
            1. If _newLength_ &gt; _totalLength_, throw a *RangeError* exception.
          1. Else,
            1. Let _newLength_ be _totalLength_.
          1. Let _A_ be a TypedArray that is an instance of _C_ with a length of _newLength_, containing the concatenated elements from _arrayList_ in order, truncated to _newLength_ elements.
          1. Return _A_.
        </emu-alg>
        <emu-note>
          <p>This method requires that the *this* value be a TypedArray constructor and that all elements of _items_ be TypedArrays of the same type. For example, `Uint8Array.concat([a, b])` requires that both _a_ and _b_ are `Uint8Array` instances.</p>
          <p>If the optional _length_ parameter is provided and is less than the sum of the lengths of all input TypedArrays, the result is truncated to the specified length. If _length_ is greater than the total length of input arrays, a *RangeError* is thrown.</p>
          <p>Implementations may use any technique to allocate and populate the result TypedArray, such as direct memory copy, deferred concatenation, or element-by-element copying, provided the observable result is a TypedArray containing the concatenated elements in order.</p>
        </emu-note>
      </emu-clause>
    </emu-clause>
  </emu-clause>
</emu-clause>